@dan Yes, switching to database search engine solved my issue.

@dan Yes, switching to database search engine solved my issue.

I'm using Elastic Search 6.3.1, currently having less than 20 users. I switched to use database search instead of Elastic. I'll switch back to elastic later.

Got an exception in the console finally:

Jul 24, 2020 3:14:36.612 AM ERROR com.inversoft.scheduler.LogAndRetainFailureHandler - The scheduled service [class io.fusionauth.api.service.user.UserReaper] failed but will be re-run.
com.inversoft.search.SearchEngineRequestFailedException: org.elasticsearch.client.ResponseException: method [GET], host [http://search:9200], URI [/fusionauth_user/_doc/_search], status line [HTTP/1.1 400 Bad Request]
{"error":{"root_cause":[{"type":"illegal_argument_exception","reason":"Fielddata is disabled on text fields by default. Set fielddata=true on [fullName] in order to load fielddata in memory by uninverting the inverted index. Note that this can however use significant memory. Alternatively use a keyword field instead."}],"type":"search_phase_execution_exception","reason":"all shards failed","phase":"query","grouped":true,"failed_shards":[{"shard":0,"index":"fusionauth_user","node":"tCJ-7yFWTu-Ilu8ckHGhmA","reason":{"type":"illegal_argument_exception","reason":"Fielddata is disabled on text fields by default. Set fielddata=true on [fullName] in order to load fielddata in memory by uninverting the inverted index. Note that this can however use significant memory. Alternatively use a keyword field instead."}}],"caused_by":{"type":"illegal_argument_exception","reason":"Fielddata is disabled on text fields by default. Set fielddata=true on [fullName] in order to load fielddata in memory by uninverting the inverted index. Note that this can however use significant memory. Alternatively use a keyword field instead.","caused_by":{"type":"illegal_argument_exception","reason":"Fielddata is disabled on text fields by default. Set fielddata=true on [fullName] in order to load fielddata in memory by uninverting the inverted index. Note that this can however use significant memory. Alternatively use a keyword field instead."}}},"status":400}
	at com.inversoft.search.AbstractElasticSearchSearchEngine.request(AbstractElasticSearchSearchEngine.java:195)
	at com.inversoft.search.AbstractElasticSearchSearchEngine.request(AbstractElasticSearchSearchEngine.java:216)
	at io.fusionauth.api.service.search.ElasticsearchSearchEngine.executeSearch(ElasticsearchSearchEngine.java:333)
	at io.fusionauth.api.service.search.ElasticsearchSearchEngine.searchByQueryString(ElasticsearchSearchEngine.java:241)
	at io.fusionauth.api.service.user.DefaultUserService.deleteBySearch(DefaultUserService.java:602)
	at io.fusionauth.api.service.user.DefaultUserService.deleteUnverifiedEmailUsers(DefaultUserService.java:664)
	at io.fusionauth.api.service.user.UserReaper.lambda$run$0(UserReaper.java:50)
	at java.base/java.util.ArrayList.forEach(ArrayList.java:1510)
	at io.fusionauth.api.service.user.UserReaper.run(UserReaper.java:41)
	at com.inversoft.scheduler.InjectableRunnable.run(InjectableRunnable.java:37)
	at java.base/java.util.concurrent.Executors$RunnableAdapter.call(Executors.java:515)
	at java.base/java.util.concurrent.FutureTask.runAndReset(FutureTask.java:305)
	at java.base/java.util.concurrent.ScheduledThreadPoolExecutor$ScheduledFutureTask.run(ScheduledThreadPoolExecutor.java:305)
	at java.base/java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1130)
	at java.base/java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:630)
	at java.base/java.lang.Thread.run(Thread.java:832)
Caused by: org.elasticsearch.client.ResponseException: method [GET], host [http://search:9200], URI [/fusionauth_user/_doc/_search], status line [HTTP/1.1 400 Bad Request]
{"error":{"root_cause":[{"type":"illegal_argument_exception","reason":"Fielddata is disabled on text fields by default. Set fielddata=true on [fullName] in order to load fielddata in memory by uninverting the inverted index. Note that this can however use significant memory. Alternatively use a keyword field instead."}],"type":"search_phase_execution_exception","reason":"all shards failed","phase":"query","grouped":true,"failed_shards":[{"shard":0,"index":"fusionauth_user","node":"tCJ-7yFWTu-Ilu8ckHGhmA","reason":{"type":"illegal_argument_exception","reason":"Fielddata is disabled on text fields by default. Set fielddata=true on [fullName] in order to load fielddata in memory by uninverting the inverted index. Note that this can however use significant memory. Alternatively use a keyword field instead."}}],"caused_by":{"type":"illegal_argument_exception","reason":"Fielddata is disabled on text fields by default. Set fielddata=true on [fullName] in order to load fielddata in memory by uninverting the inverted index. Note that this can however use significant memory. Alternatively use a keyword field instead.","caused_by":{"type":"illegal_argument_exception","reason":"Fielddata is disabled on text fields by default. Set fielddata=true on [fullName] in order to load fielddata in memory by uninverting the inverted index. Note that this can however use significant memory. Alternatively use a keyword field instead."}}},"status":400}
	at org.elasticsearch.client.RestClient.convertResponse(RestClient.java:283)
	at org.elasticsearch.client.RestClient.performRequest(RestClient.java:261)
	at org.elasticsearch.client.RestClient.performRequest(RestClient.java:235)
	at com.inversoft.search.AbstractElasticSearchSearchEngine.request(AbstractElasticSearchSearchEngine.java:192)
	... 15 common frames omitted
Jul 24, 2020 6:14:36.539 AM ERROR com.inversoft.scheduler.LogAndRetainFailureHandler - The scheduled service [class io.fusionauth.api.service.user.UserReaper] failed AGAIN! The service will still continue to run, but we are going to stop logging the errors.
25-Jul-2020 16:09:02.138 INFO [http-nio-9011-exec-16] org.apache.coyote.http11.Http11Processor.service Error parsing HTTP request header
 Note: further occurrences of HTTP request parsing errors will be logged at DEBUG level.
	java.lang.IllegalArgumentException: Invalid character found in method name. HTTP method names must be tokens
		at org.apache.coyote.http11.Http11InputBuffer.parseRequestLine(Http11InputBuffer.java:432)
		at org.apache.coyote.http11.Http11Processor.service(Http11Processor.java:502)
		at org.apache.coyote.AbstractProcessorLight.process(AbstractProcessorLight.java:65)
		at org.apache.coyote.AbstractProtocol$ConnectionHandler.process(AbstractProtocol.java:818)
		at org.apache.tomcat.util.net.NioEndpoint$SocketProcessor.doRun(NioEndpoint.java:1623)
		at org.apache.tomcat.util.net.SocketProcessorBase.run(SocketProcessorBase.java:49)
		at java.base/java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1130)
		at java.base/java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:630)
		at org.apache.tomcat.util.threads.TaskThread$WrappingRunnable.run(TaskThread.java:61)
		at java.base/java.lang.Thread.run(Thread.java:832)
27-Jul-2020 23:48:59.250 INFO [http-nio-9011-exec-38] org.apache.coyote.http11.Http11Processor.service Error parsing HTTP request header
 Note: further occurrences of HTTP request parsing errors will be logged at DEBUG level.
	java.lang.IllegalArgumentException: Invalid character found in method name. HTTP method names must be tokens
		at org.apache.coyote.http11.Http11InputBuffer.parseRequestLine(Http11InputBuffer.java:432)
		at org.apache.coyote.http11.Http11Processor.service(Http11Processor.java:502)
		at org.apache.coyote.AbstractProcessorLight.process(AbstractProcessorLight.java:65)
		at org.apache.coyote.AbstractProtocol$ConnectionHandler.process(AbstractProtocol.java:818)
		at org.apache.tomcat.util.net.NioEndpoint$SocketProcessor.doRun(NioEndpoint.java:1623)
		at org.apache.tomcat.util.net.SocketProcessorBase.run(SocketProcessorBase.java:49)
		at java.base/java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1130)
		at java.base/java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:630)
		at org.apache.tomcat.util.threads.TaskThread$WrappingRunnable.run(TaskThread.java:61)
		at java.base/java.lang.Thread.run(Thread.java:832)

@dan I am using PostgreSQL, indeed. I don't think the data has any special character to cause this issue, but I could check this out.

@dan This issue happens on Chrome (Version 84.0.4147.89 (Official Build) (64-bit)) and Safari as-well. The data of user contains user information, such as phone number, address, and just a bunch of short strings (street name, etc.) Let me know if there are some steps I could take to provide you with more debugging information.

I get no errors in the terminal where I'm running docker, I just checked the browser for errors and I get:

Failed to load resource: the server responded with a status of 400 ()

This is the request URL:
{fauth_link}/ajax/user/search?s.sortFields%5B0%5D.name=login&s.sortFields%5B0%5D.order=asc&s.sortFields%5B1%5D.name=fullName&s.sortFields%5B1%5D.order=asc

Every time I try to access the "Users" tab in the Fusion Auth admin panel, I get an "Error" popup with no more details. The exact text is "FusionAuth encountered an error while processing your request. If the problem persists, contact FusionAuth support for assistance.". I see no errors in the console.

I'm running fusion auth with docker.

OS: Ubuntu 16.04.5 LTS
Fusion Auth version: 1.18.2
Docker version: 18.09.6, build 481bc77