There’s no error 406 in this log. Now that I remember there’s an issue with some servers that redirect urls to other urls - see here: Latest android Joplin began to fail WebDav synchronization
It’s unnecessary and inefficient for an API to do that but some servers do it anyway, so maybe that’s your issue. Unfortunately there’s no plan for a fix for now as this would bring a lot of additional complexity just to support servers that shouldn’t have this redirection in the first place.