403 error?There’s a laundry list of changes and cautions about the update here:
Including this line that should be in bold: After installing DSM 7.0.1, you will not be able to downgrade to a previous DSM version.
There was one thread on it, but no resolution I’m aware of.
I’m using DSM 7.0 as a sync store for DT via WebDAV. And my DT(TG) installs are all in sync, so I suppose it’s working 
Haven’t upgraded to 7.0.1 yet (the automatic upgrade failed, no idea why).
Edit: The release notes do not mention WebDAV at all. Login problems might be related to the TLS/SSL changes, but I didn’t notice anything. Even SMB works as before.
That’s what I was suspecting as well and thanks for sharing the info on a lack of interruption in syncing.
I’m running DSM 7.0.1-42218 and DT ( also DTTG) with WebDAV sync works great.
Did you update from 6.x → 7.0.1 or 7.0 → 7.0.1?
7.0 > 7.0.1
I’m not sure if WebDAV was updated with 7.0.1. The update information in the package center on my DS218+ is: 2021-07-02 with version 2.4.1-10108.
Thanks for the clarification 
Just upgraded to 7.0.1. WebDAV works without a change.
Excellent! Thanks for the follow-up.
FYI, just this afternoon upgraded DSM 7.0 to 7.0.1 and all the important stuff I checked seem to work: WebDAV for DEVONthink sync, TimeMachine backup via SMB, a web server, Hyperbackup, CloudSync, and “plain old” file access.
The upgrade faster than promised in the Release notes.
Good to hear. Thanks!
I followed this path, as shown by Bluefrog: 6.x → 7.0 → 7.0.1 across time and working without any issue.
Excellent! Thanks for sharing that info.
The path 6.x → 7.0 → 7.0.1, with DT (and DTTG) with WebDAV without any issue…