If I look at the first error log I reported, I saw something interesting. There was an owncloud message there:
019-11-28 12:34:22: “Req 12:33:47: PROPFIND https://webdav.pcloud.com/Joplin/(...).md {“headers”:{“Depth”:0,“Authorization”:”********",“If-None-Match”:“JoplinIgnore-28618”,“Content-Length”:“190”},“body”:"<?xml version=\"1.0\" encoding=\"UTF-8\"?>\n\t\t\t<d:propfind xmlns:d=“DAV:”>\n\t\t\t\t<d:prop xmlns:oc="http://owncloud.org/ns">\n\t\t\t\t\t<d:getlastmodified/><d:resourcetype/>\n\t\t\t\t</d:prop>\n\t\t\t</d:propfind>",“timeout”:120000,“maxRetry”:0}"
2019-11-28 12:34:22: "Res 12:33:47:
404 Not Found
Is this message coming from pcloud or from Joplin? If it is pcloud then does this mean that pcloud is running owncloud?