dovecot - Apr 2017 - Extension record update for invalid uid=

Hi list

yesterday I got many of these errors:

Error: Log synchronization error at seq=832,offset=2348 for  
indexes/.INBOX/dovecot.index: Extension record update for invalid  
uid=29175

But just for __ONE__ user.

I couldn't find any misconfiguration for this user, it's just all
other...

Can someone say what it happens and how can I fix it?

Thanks
Luca Bertoncello
(lucabert at lucabert.de)