Error: PUT Unknown error 2 (507)

Windows 10, Joplin 1.1.4

Hi, I just installed Joplin today on Android and Windows 10. At first it worked with encrypted syncing via Webdav on mailbox.org. Then I imported a lot of notes from Evernote. But now I get the following error and syncing isn't working anymore. What could be the problem?

Remote-Elemente erstellt: 1.

Abgeschlossen: 21.09.2020 23:06

Letzte Fehlermeldung: Error: PUT .resource/262eefb9e95a4cee905dac591a193fd6: Unknown error 2 (507):