I accidentally wrote something and then deleted it in the upper section of Nextcloud web portal for a particualr folder. After this, the sync client started throwing this error message which I think the Readme.md file has to do with that section that you can add comments.
I tried disabling the “Show Richtext” optino and still get this error.
I have the same error. I am looking for a solution too. If I fix it I’ll write to you !!!
In server, run :
cd /var/www/nextcloud (Change to your folder with nextcloud)
sudo -u www-data php occ files:scan --all
[ www-data or User configured in Apache or Nginx ]
This helped, I tried it out!
Also I tried by unsyncing the specific folder and it got fixed. So I deleted it, and recreated it…then synced it back. A lot more work than yours, but I think both of these methods are good solutions.