Occasionally, our users are receiving an error that says "The operation requires that the document be checked out first. [9100]".  When the error occurs, the one thing that seems to be a commonality is that the user has added an annotation.  In most cases, after the answer Ok is selected, all changes, including the annotation, are saved.  Although I have witnessed one case where the changes did not stick.  

I have tried numerous workarounds and am unable to resolve the issue.    

The saving of the changes does kick off a Workflow process.  The workflow process does not make changes to the document or the metadata, it sends an email to a user (specified in a dropdown in the metadata).  Not sure if this has anything to do with the problem or not.

The users have been doing this type of work for about six months and the problem only started happening about 2 weeks ago. I believe it has happened about 6 - 10 times so far.

We are using Laserfiche Web Client, version 10.4.2.347 and Repository Access version 10.4.2.73.  We are self-hosted.