@Burlakov Eduard After going through your Atlassian Confluence log file, There are lots of errors.
Found some interesting stuff, JavaOutOfMemoryError caused by the scroll word exporter plugin, by K15t
2020-03-16 14:30:11,934 ERROR [scroll-exporter-download:thread-2] [scroll.exporter.util.ExportThreadFactory] lambda$newThread$0 Unexpected error in thread Thread[scroll-exporter-download:thread-2,5,scroll-exporter-download]
java.lang.OutOfMemoryError: Java heap space
You would need to increase Java memory, How to fix out of memory errors by increasing available memory
The gap in the log before the getWorkflows error started generating is interesting almost 7mins
2020-03-13 18:03:54,396 ERROR [https-jsse-nio2-443-exec-11] [[Standalone].[localhost].[/].[noop]] log Servlet.service() for servlet [noop] in context with path  threw exception
2020-03-13 18:10:18,673 ERROR [https-jsse-nio2-443-exec-9] [comalatech.confluence.workflow.DefaultWorkflowAccessor] getWorkflows
2020-03-13 18:10:18,676 ERROR [https-jsse-nio2-443-exec-9] [confluence.workflow.listeners.TriggersListener] handleEvent com.atlassian.confluence.pages.Attachment cannot be cast to com.atlassian.confluence.pages.AbstractPage
2020-03-13 18:12:54,421 ERROR [https-jsse-nio2-443-exec-1] [comalatech.confluence.workflow.DefaultWorkflowAccessor] getWorkflows
2020-03-13 18:12:54,427 ERROR [https-jsse-nio2-443-exec-1] [confluence.workflow.listeners.TriggersListener] handleEvent com.atlassian.confluence.pages.Attachment cannot be cast to com.atlassian.confluence.pages.AbstractPage
2020-03-13 18:55:07,830 ERROR [Caesium-1-4] [atlassian.crowd.directory.DbCachingDirectoryPoller] pollChanges Error occurred while refreshing the cache for directory [ 15532033 ].
Before and after this error, There is some pool changes error with refreshing db cache directory . I think you have a Comala Workflow for confluence plugin . As i know the plugin is now Comala Document Management.
PLEASE disable this plugin or UN-install it completely
Stop and Restart Confluence and monitor your instance to see if this was the root cause.
The below error also appears a lot of times
2020-03-13 11:56:37,689 ERROR [https-jsse-nio2-443-exec-1] [core.persistence.hibernate.HibernateObjectDao] findSingleObject Uh oh - found more than one object when single object requested: [Attachment: user-avatar v.1 (6325449) guest-rnd, Attachment: user-avatar v.1 (6325450) guest-rnd]
You may also want to fix the error there are multiple versions of V.1 for this user avatar you will need remove duplicate. I suspect that the Username is guest-rnd not certain. follow article here to find content id and there is path to this attachment mention in article.
It took lots of time to get reponse from request to Opserver.2.rb.local running at port 88
2020-03-13 10:15:47,197 ERROR [https-jsse-nio2-443-exec-25] [plugins.macros.html.WhitelistedHttpRetrievalMacro] execute Unable to get HTTP response from http://opserver2.rb.local:88/html/rd?path=Current
You added a whietlist in confluence for this link http://opserver2.rb.local:88/html/rd?path=Current . you may want to verify if this server is working.
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