I am ignorant of all this, but thinking like a detective, I went and searched the code for WebDAV:
https://github.com/salesagility/SuiteCRM/search?utf8=âś“&q=webdav&type=
It seems it’s all Calendar related stuff (iCal). So maybe it’s your Calendar Dashlet. You can go in the Calendar module and see if you also get that prompt there.
Check your user profile options about iCal URL’s, etc.
Good luck and please share your findings when you solve this.