Synchronisation not working (Win10/Nextcloud) - Android OK

Windows 10 Home / Joplin v1.0.75 (install and portable) as well as 1.0.69 (portable)

Android 1.0.312 - Synchronisation works great, no issues.

Nextcloud 15.0.14

Paths and Credentials are identical, no hidden spaces or typos. Tried with different users and directories, empty or not.

On nextcloud, it creates directories:

.sync
.resource

Both are empty. This is also mentioned in the logfile:

2019-12-29 12:45:11: "Preparing scheduled sync"
2019-12-29 12:45:11: "Starting scheduled sync"
2019-12-29 12:45:12: "Sync: starting: Starting synchronisation to target 6... [1577619911577]"
2019-12-29 12:45:12: "mkdir .sync"
2019-12-29 12:45:12: "mkdir .resource"

Then I get this error looping:

    2019-12-29 12:51:18: "Preparing scheduled sync"
2019-12-29 12:51:18: "Starting scheduled sync"
2019-12-29 12:51:38: "ResourceService::indexNoteResources: Start"
2019-12-29 12:51:38: "ResourceService::indexNoteResources: Completed"
2019-12-29 12:51:38: "ResourceService::deleteOrphanResources:", "[]"
2019-12-29 12:51:42: "Error: PROPFIND .lock/: Unknown error 2 (403): <HTML>
<HEAD>
<TITLE>403 Forbidden</TITLE>
<BASE href="/error_docs/"><!--[if lte IE 6]></BASE><![endif]-->
</HEAD>
<BODY>
<H1>Forbidden</H1>
You do not have permission to access this document.
<P>
<HR>
<ADDRESS>
Web Server at xxx.yy.my-provider.de
</ADDRESS>
</BODY>
</HTML>

<!--
   - Unfortunately, Microsoft has added a clever new
   - "feature" to Internet Explorer. If the text of
   - an error's message is "too small", specifically
   - less than 512 bytes, Internet Explorer returns
   - its own error message. You can turn that off,
   - but it's pretty tricky to find switch called
   - "smart error messages". That means, of course,
   - that short error messages are censored by default.
   - IIS always returns error messages that are long
   - enough to make Internet Explorer happy. The
   - workaround is pretty simple: pad the error
   - message with a big comment like this to push it
   - over the five hundred and twelve bytes minimum.
   - Of course, that's exactly what you're reading
   - righ
Code: 403
Error: PROPFIND .lock/: Unknown error 2 (403): <HTML>
<HEAD>
<TITLE>403 Forbidden</TITLE>
<BASE href="/error_docs/"><!--[if lte IE 6]></BASE><![endif]-->
</HEAD>
<BODY>
<H1>Forbidden</H1>
You do not have permission to access this document.
<P>
<HR>
<ADDRESS>
Web Server at xxx.yy.my-provider.de
</ADDRESS>
</BODY>
</HTML>

<!--
   - Unfortunately, Microsoft has added a clever new
   - "feature" to Internet Explorer. If the text of
   - an error's message is "too small", specifically
   - less than 512 bytes, Internet Explorer returns
   - its own error message. You can turn that off,
   - but it's pretty tricky to find switch called
   - "smart error messages". That means, of course,
   - that short error messages are censored by default.
   - IIS always returns error messages that are long
   - enough to make Internet Explorer happy. The
   - workaround is pretty simple: pad the error
   - message with a big comment like this to push it
   - over the five hundred and twelve bytes minimum.
   - Of course, that's exactly what you're reading
   - righ
    at newError (C:\Users\SERVI_~1\AppData\Local\Temp\nspA53A.tmp\app\resources\app.asar\lib\WebDavApi.js:393:11)
    at WebDavApi.exec (C:\Users\SERVI_~1\AppData\Local\Temp\nspA53A.tmp\app\resources\app.asar\lib\WebDavApi.js:423:10)
    at process._tickCallback (internal/process/next_tick.js:68:7)"
2019-12-29 12:51:42: "Req 12:51:18: MKCOL https://cloud.***********.de/remote.php/webdav/JoplinWeb/.sync/ {"headers":{"Authorization":"********","If-None-Match":"JoplinIgnore-90958","User-Agent":"Joplin/1.0"},"timeout":120000,"maxRetry":0}"
2019-12-29 12:51:42: "Res 12:51:18: <?xml version="1.0" encoding="utf-8"?>
<d:error xmlns:d="DAV:" xmlns:s="http://sabredav.org/ns">
  <s:exception>Sabre\DAV\Exception\MethodNotAllowed</s:exception>
  <s:message>The resource you tried to create already exists</s:message>
</d:error>
"
2019-12-29 12:51:42: "Req 12:51:19: MKCOL https://cloud.***********.de/remote.php/webdav/JoplinWeb/.lock/ {"headers":{"Authorization":"********","If-None-Match":"JoplinIgnore-31394","User-Agent":"Joplin/1.0"},"timeout":120000,"maxRetry":0}"
2019-12-29 12:51:42: "Res 12:51:19: "
2019-12-29 12:51:42: "Req 12:51:19: MKCOL https://cloud.***********.de/remote.php/webdav/JoplinWeb/.resource/ {"headers":{"Authorization":"********","If-None-Match":"JoplinIgnore-21675","User-Agent":"Joplin/1.0"},"timeout":120000,"maxRetry":0}"
2019-12-29 12:51:42: "Res 12:51:19: <?xml version="1.0" encoding="utf-8"?>
<d:error xmlns:d="DAV:" xmlns:s="http://sabredav.org/ns">
  <s:exception>Sabre\DAV\Exception\MethodNotAllowed</s:exception>
  <s:message>The resource you tried to create already exists</s:message>
</d:error>
"
2019-12-29 12:51:42: "Req 12:51:19: PROPFIND https://cloud.***********.de/remote.php/webdav/JoplinWeb/.lock/ {"headers":{"Depth":1,"Authorization":"********","If-None-Match":"JoplinIgnore-52401","User-Agent":"Joplin/1.0","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}"
2019-12-29 12:51:42: "Res 12:51:19: <HTML>
<HEAD>
<TITLE>403 Forbidden</TITLE>
<BASE href="/error_docs/"><!--[if lte IE 6]></BASE><![endif]-->
</HEAD>
<BODY>
<H1>Forbidden</H1>
You do not have permission to access this document.
<P>
<HR>
<ADDRESS>
Web Server at xxx.yy.my-provider.de
</ADDRESS>
</BODY>

I can provide more logs if needed.
Is there any difference between android sync and Windows-Sync? I also tried the “Webdav”-way. Didn’t work either.

I’m out of options now. Would be great if one could help, as I love joplin!

Replying to my own question: I got it working on another Nextcloud.
Differences are: Nextcloud v17.0.1 / Different provider.

Gonna try to update the other nextcloud to 17.0.1 and test again.