[Evolution] Too many user defined flags

[Paulo Cesar Costa <paulo costafamily org>]

All:

I am getting an error that is new for me and one I was not able to
figure out searching in the documentation:

> Error syncing changes: too many user defined flags

I did not change the number of labels at:
> Preferences>Mail Preferences>Labels

The error happens in the imap account I use to store my messages via
Evolution Filters. That is, I have 8 imap accounts and in most cases
the incoming messages are filtered out by subject and stored in this
one account (for which I have no quota restrictions).

I may be misunderstanding the meaning of the message. Here are my
hypotheses so far:

1) Something related to the total number of labels defined in the
above-mentioned menu
- I did not change the labels and the system has been working without
issues long after the last label I changed

2) Something related to the number of labels set to a single message
- I did not find references to a limit on the number of labels a
message receives. Yet, this is something I am still exploring


3) Something related to inconsistencies in how the filter rules work
(e.g. one filter sends message X to a folder while other filter tries
to send to a different one)
- Exploring this, but so far I found no inconsistency. I did not change
the rules for a while so this seems unlikely too.

4) A conflict between imap labels and internal evolution ones.
- I found a few messages in the list about it, such as this one:
https://mail.gnome.org/archives/evolution-list/2015-December/msg00066.html
Yet, I see no evidence that this might be the cause.

5) Something else
- No further ideas. This is why I am asking for help here...


More importantly, any hints on how to troubleshoot this? I tried
starting from the terminal to see any error messages but nothing
appeared so far.
My next step will be to remove all the labels and run the filters
again. 

Thank you,
Paulo

Evolution: 3.40.3 (3.40.3-1.fc34) 
Kernel: 5.13.4-200.fc34.x86_64 
OS: Fedora release 34 (Thirty Four) x86_64