I use Foldersync, the developer clearly stated he was not maintaining it anymore, so it’s unlikely it’s caused by an upgrade on Foldersync side.
Last night, my Seafile got upgraded to 7.1.3, and Foldersync started failing (reported here Seafdav 502 Bad Gateway after upgrade to 7.1.3 yesterday (Docker))
It is definitely related to 7.1.x webdav breaking.