Requests being rejected with "Invalid user"

[Dan M]

We have been running FreeRadius for about 18 months with very light traffic
and no issues.
Recently, within the last month, some requests are rejected and a message
appears in the log 
Invalid user: [the actual user id] (from client <the actual client id> port
0)

It seems completely random.
The end user just hits enter again which runs thru the client system and
generates a new request that succeeds.
(Well it seems that none of the second requests have failed.  I have no
reports otherwise)
The user id seems to me to be identical (at least in the log) for both the
failure and the success. 

This happened on multiple instances in multiple locations.
Restarting the instances seemed to clear the issue for a while, but it's
resurfaced (after about 12 days).

I do not think that the request is getting to the "authorize" phase because
there is no message from the python plug-in indicating that it started.
So maybe this comes from some pre-authorize step?

I scanned all the configuration and don't find that string "Invalid user"
anywhere, 
so I'm thinking it's generated internally when something else fails.

Unfortunately, this is in a locked-down, production environment and I can't
just "start it up in debug mode"
Is this something you have seen before?
Is there something I might do to increase the log level?  Where, how, and of
what?

We are running version 3.0.17.

Dan Mullen


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