I have configured a unique Crowd directory in Jira Server with the following configuration:

Since yesterday, when we try to synchronize we get the following error message:
Synchronisation failed. See server logs for details.
We have checked the atlassian-jira.log file and found out the following trace. We don´t understand what is going on and we really appreciate it if somebody her can give us an advice:
2-15 15:38:38,758+0100 Caesium-1-1 INFO ServiceRunner [c.a.crowd.directory.DbCachingRemoteDirectory] INCREMENTAL synchronisation for directory [ 10500 ] starting
2021-12-15 15:38:38,758+0100 Caesium-1-1 INFO ServiceRunner [c.a.crowd.directory.DbCachingRemoteDirectory] Attempting INCREMENTAL synchronisation for directory [ 10500 ]
2021-12-15 15:38:38,758+0100 Caesium-1-1 DEBUG ServiceRunner [c.a.c.d.ldap.cache.EventTokenChangedCacheRefresher] A full synchronisation is needed to obtain the current token event
2021-12-15 15:38:38,758+0100 Caesium-1-1 INFO ServiceRunner [c.a.crowd.directory.DbCachingRemoteDirectory] Incremental synchronisation for directory [ 10500 ] was not completed, falling back to a full synchronisation
2021-12-15 15:38:38,758+0100 Caesium-1-1 INFO ServiceRunner [c.a.crowd.directory.DbCachingRemoteDirectory] INCREMENTAL synchronisation for directory [ 10500 ] was not successful, attempting FULL
2021-12-15 15:38:39,020+0100 Caesium-1-1 WARN ServiceRunner [c.a.c.d.ldap.cache.EventTokenChangedCacheRefresher] Incremental synchronisation is not available. Falling back to full synchronisation
com.atlassian.crowd.event.IncrementalSynchronisationNotAvailableException
at com.atlassian.crowd.integration.rest.service.RestCrowdClient.getCurrentEventToken(RestCrowdClient.java:1002)
at com.atlassian.crowd.directory.RemoteCrowdDirectory.getCurrentEventToken(RemoteCrowdDirectory.java:631)
at com.atlassian.crowd.directory.ldap.cache.EventTokenChangedCacheRefresher.synchroniseAll(EventTokenChangedCacheRefresher.java:47)
at com.atlassian.crowd.directory.DbCachingRemoteDirectory.synchroniseCache(DbCachingRemoteDirectory.java:978)
at com.atlassian.crowd.manager.directory.DirectorySynchroniserImpl.synchronise(DirectorySynchroniserImpl.java:67)
at com.atlassian.jira.crowd.embedded.JiraDirectorySynchroniser.synchronizeDirectory(JiraDirectorySynchroniser.java:77)
at com.atlassian.jira.crowd.embedded.JiraDirectorySynchroniser.runJob(JiraDirectorySynchroniser.java:52)
at com.atlassian.scheduler.core.JobLauncher.runJob(JobLauncher.java:134)
at com.atlassian.scheduler.core.JobLauncher.launchAndBuildResponse(JobLauncher.java:106)
at com.atlassian.scheduler.core.JobLauncher.launch(JobLauncher.java:90)
at com.atlassian.scheduler.caesium.impl.CaesiumSchedulerService.launchJob(CaesiumSchedulerService.java:435)
at com.atlassian.scheduler.caesium.impl.CaesiumSchedulerService.executeClusteredJob(CaesiumSchedulerService.java:430)
at com.atlassian.scheduler.caesium.impl.CaesiumSchedulerService.executeClusteredJobWithRecoveryGuard(CaesiumSchedulerService.java:454)
at com.atlassian.scheduler.caesium.impl.CaesiumSchedulerService.executeQueuedJob(CaesiumSchedulerService.java:382)
at com.atlassian.scheduler.caesium.impl.SchedulerQueueWorker.executeJob(SchedulerQueueWorker.java:66)
at com.atlassian.scheduler.caesium.impl.SchedulerQueueWorker.executeNextJob(SchedulerQueueWorker.java:60)
at com.atlassian.scheduler.caesium.impl.SchedulerQueueWorker.run(SchedulerQueueWorker.java:35)
at java.lang.Thread.run(Thread.java:748)
Thanks,