Error: POST files/list_folder: Error (409)

I have this error now (both on my computer and on the Android client) :

Completed: 05/07/2021 10:40 (23s)

Last error: Error: POST files/list_folder: Error (409): {"error_summary": "path/not_found/.", "error": {".tag": "path", "path": {".tag": "not_found"}}}

One problem with this message is that it doesn't specify which path it tries to access… That would help fixing it.

My synchronization mode is "Dropbox".

This might be related to the fact I excluded some folders from sync, as explained in Joplin, I love you... but this is driving me nuts (Dropbox) - #3 by Sophia and following. I might have excluded one too much folder…
Apparently, I have to find out on which computer I excluded the folders, because Dropbox won't show them anymore…