Failed to load the cache in 5 attempts - flush not working anymore

Hi,

We’re currently experiencing a problem with one of our users. This seems to be limited only to him, and we are not sure why this is the case. He cannot log in at all anymore.

2020-11-16 11:53:17,030 [http://doku.atenekom.eu/bin/skin/XWiki/DefaultSkin/atene_logo.png] ERROR c.i.DefaultSecurityCacheLoader - Failed to load the cache in 5 attempts. Giving up.
2020-11-16 11:53:17,030 [http://doku.atenekom.eu/bin/skin/XWiki/DefaultSkin/atene_logo.png] ERROR a.i.BridgeAuthorizationManager - Failed to load rights for user [xwiki:XWiki.username] on [xwiki:XWiki.Notifications.Code.NotificationsDisplayerUIX].
org.xwiki.security.authorization.AuthorizationException: Failed to load the cache in 5 attempts. Giving up. when checking  access to [xwiki:XWiki.Notifications.Code.NotificationsDisplayerUIX] for user [xwiki:XWiki.username]
	at org.xwiki.security.authorization.cache.internal.DefaultSecurityCacheLoader.load(DefaultSecurityCacheLoader.java:168)
	at org.xwiki.security.authorization.DefaultAuthorizationManager.getAccess(DefaultAuthorizationManager.java:218)
	at org.xwiki.security.authorization.DefaultAuthorizationManager.evaluateSecurityAccess(DefaultAuthorizationManager.java:159)
	at org.xwiki.security.authorization.DefaultAuthorizationManager.hasSecurityAccess(DefaultAuthorizationManager.java:152)
	at org.xwiki.security.authorization.DefaultAuthorizationManager.hasAccess(DefaultAuthorizationManager.java:109)
	at org.xwiki.security.authorization.internal.BridgeAuthorizationManager.hasAccess(BridgeAuthorizationManager.java:67)
	at org.xwiki.security.authorization.internal.DefaultContextualAuthorizationManager.hasAccess(DefaultContextualAuthorizationManager.java:122)
	at org.xwiki.security.authorization.internal.DefaultContextualAuthorizationManager.hasAccess(DefaultContextualAuthorizationManager.java:117)
	at com.xpn.xwiki.plugin.skinx.AbstractDocumentSkinExtensionPlugin.isAccessible(AbstractDocumentSkinExtensionPlugin.java:390)
	at com.xpn.xwiki.plugin.skinx.CssSkinExtensionPlugin.getLink(CssSkinExtensionPlugin.java:80)
	at com.xpn.xwiki.plugin.skinx.AbstractSkinExtensionPlugin.getImportString(AbstractSkinExtensionPlugin.java:295)
	at com.xpn.xwiki.plugin.skinx.AbstractSkinExtensionPlugin.endParsing(AbstractSkinExtensionPlugin.java:396)
	at com.xpn.xwiki.plugin.skinx.AbstractDocumentSkinExtensionPlugin.endParsing(AbstractDocumentSkinExtensionPlugin.java:281)
	at com.xpn.xwiki.plugin.skinx.CssSkinExtensionPlugin.endParsing(CssSkinExtensionPlugin.java:114)
	at com.xpn.xwiki.plugin.XWikiPluginManager.endParsing(XWikiPluginManager.java:272)
	at com.xpn.xwiki.web.Utils.parseTemplate(Utils.java:183)
	at com.xpn.xwiki.web.Utils.parseTemplate(Utils.java:88)
	at com.xpn.xwiki.web.XWikiAction.execute(XWikiAction.java:540)
	at com.xpn.xwiki.web.XWikiAction.execute(XWikiAction.java:218)
	at org.apache.struts.action.RequestProcessor.processActionPerform(RequestProcessor.java:425)
	at org.apache.struts.action.RequestProcessor.process(RequestProcessor.java:228)
	at org.apache.struts.action.ActionServlet.process(ActionServlet.java:1913)
	at org.apache.struts.action.ActionServlet.doGet(ActionServlet.java:449)
	at javax.servlet.http.HttpServlet.service(HttpServlet.java:634)
	at javax.servlet.http.HttpServlet.service(HttpServlet.java:741)
	at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:231)
	at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:166)
	at com.xpn.xwiki.web.ActionFilter.doFilter(ActionFilter.java:112)
	at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:193)
	at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:166)
	at org.xwiki.wysiwyg.filter.ConversionFilter.doFilter(ConversionFilter.java:109)
	at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:193)
	at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:166)
	at org.xwiki.container.servlet.filters.internal.SetHTTPHeaderFilter.doFilter(SetHTTPHeaderFilter.java:63)
	at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:193)
	at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:166)
	at org.xwiki.container.servlet.filters.internal.SavedRequestRestorerFilter.doFilter(SavedRequestRestorerFilter.java:208)
	at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:193)
	at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:166)
	at org.xwiki.container.servlet.filters.internal.SetCharacterEncodingFilter.doFilter(SetCharacterEncodingFilter.java:111)
	at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:193)
	at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:166)
	at org.xwiki.resource.servlet.RoutingFilter.doFilter(RoutingFilter.java:132)
	at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:193)
	at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:166)
	at org.apache.catalina.core.StandardWrapperValve.invoke(StandardWrapperValve.java:199)
	at org.apache.catalina.core.StandardContextValve.invoke(StandardContextValve.java:96)
	at org.apache.catalina.authenticator.AuthenticatorBase.invoke(AuthenticatorBase.java:543)
	at org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:139)
	at org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:81)
	at org.apache.catalina.valves.AbstractAccessLogValve.invoke(AbstractAccessLogValve.java:678)
	at org.apache.catalina.core.StandardEngineValve.invoke(StandardEngineValve.java:87)
	at org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:343)
	at org.apache.coyote.http11.Http11Processor.service(Http11Processor.java:609)
	at org.apache.coyote.AbstractProcessorLight.process(AbstractProcessorLight.java:65)
	at org.apache.coyote.AbstractProtocol$ConnectionHandler.process(AbstractProtocol.java:810)
	at org.apache.tomcat.util.net.NioEndpoint$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:1128)
	at java.base/java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:628)
	at org.apache.tomcat.util.threads.TaskThread$WrappingRunnable.run(TaskThread.java:61)
	at java.base/java.lang.Thread.run(Thread.java:834)
Caused by: org.xwiki.security.authorization.cache.ConflictingInsertionException: null
	at org.xwiki.security.authorization.cache.internal.DefaultSecurityCache.isAlreadyInserted(DefaultSecurityCache.java:606)
	at org.xwiki.security.authorization.cache.internal.DefaultSecurityCache.add(DefaultSecurityCache.java:682)
	at org.xwiki.security.authorization.cache.internal.DefaultSecurityCache.add(DefaultSecurityCache.java:655)
	at org.xwiki.security.authorization.cache.internal.DefaultSecurityCacheLoader.loadUserEntry(DefaultSecurityCacheLoader.java:423)
	at org.xwiki.security.authorization.cache.internal.DefaultSecurityCacheLoader.loadUserEntry(DefaultSecurityCacheLoader.java:322)
	at org.xwiki.security.authorization.cache.internal.DefaultSecurityCacheLoader.loadAccessEntries(DefaultSecurityCacheLoader.java:225)
	at org.xwiki.security.authorization.cache.internal.DefaultSecurityCacheLoader.loadRequiredEntries(DefaultSecurityCacheLoader.java:197)
	at org.xwiki.security.authorization.cache.internal.DefaultSecurityCacheLoader.load(DefaultSecurityCacheLoader.java:150)
	... 61 common frames omitted

What did work for a while was flushing JMX and xwiki Cache. That seems to be a temporary solution and it did work for 2 or 3 times, but after a while it stopped working completely and we cannot get passed the error.
I’ve searched on the internet and I’ve seen various people having to deal with this problem, but there was definitve solutions.

We are using version 11.10.3.

Any suggestions are welcome!

Regards!