When updating from 2.3.1.140 -> 2.3.3.133 on a c5 I found I was unable to access the web interface at all, even while plugged directly into the same switch. I used the IP:8081 trick to roll back 2 versions and now I'm able to access the admin interface again.
I see a lot of threads about blocking proxy access and needing to permit non-local access, but nothing that matches this "on the same LAN and still cannot get in" behavior. Any pointers?