I have a 2710n and it's worked like a champ for years.

I have always updated the firmware quite promptly.

By chance I noticed the latest release:

Firmware Information
Current Version

3.6.9

Release Notes
Release Date 02/08/2017
Support Language English
Supported Models Vigor 2710
Vigor 2710n
Vigor 2710Vn

After 24 hours I get a sessions limit error, never even knew there was a thing. But It's disabled.

Looks like: http://www.i-helpdesk.com.au/index.php?/Knowledgebase/Article/View/594/13/how-to-fix-session-limit-reached-issue

Did the bug resurface somehow?

Another bug, on timeout I'm redirected to /cgi-bin/wlogin.cgi which 404s!

3.6.9 is suspect.

That's unfortunate that you're seeing those two issues, could you contact the DrayTek UK support team for assistance with those problems?

The second issue is strange, I don't get that 404 error when I'm logged out through time-out and the /cgi-bin/wlogin.cgi address does go to the login page.