Indexer Cluster user="" had no roles

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Hello to everyone!
Today I noticed strange messages in the daily warn and errors report:

10-04-2024 16:55:01.935 +0300 WARN  UserManagerPro [5280 indexerPipe_0] - Unable to get roles for user= because: Could not get info for non-existent user=""
10-04-2024 16:55:01.935 +0300 ERROR UserManagerPro [5280 indexerPipe_0] - user="" had no roles

I checked that this couple first appeared 5 days ago, but this fact can't help me because I don't remember what I changed in the exact day.
I also tried to find some helpful "nearby" events that can help me to understand the root case, but didn't observe anything interesting.
Which ways do I have to investigate this case?
Maybe I can "rise" log policy to DEBUG lvl? If I can, what should I change and where?

Little more information:
I have searchhead cluster with LDAP authorization
And also indexer cluster only with local users

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A week ago, I tried to enable DEBUG log to find the root case
But found only the similar events without anything helpful to find the root case

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