I can replicate the problem in multiple browsers (Chrome, Edge Chromium, Internet Explorer) on multiple devices.
I have run a repair on pi-hole - no success
I have run a reconfigure on pi-hole - no success
I have completely uninstalled, deleted all traces of pi-hole and performed a fresh install - no success
I am running pi-hole on a Virtual Machine in Hyper V, the Virtual Machine is running Ubuntu 18.04.4 LTS
This is the intended behavior. White/Blacklist are meant for easier management for inexperience user coming from v4.0 or users who have no groups configured.
To see the group assignment one has to use Group managemen/domains.
Why does it appear in the first place, albeit only once and then come back after clearing browsing data?
Why do other people not seem to have this issue, one of the mods even said they do not see this behaviour on 3 installs of pi-hole v5 and advised me to raise this ticket here (as noted in the below reddit post)?
I have this same issue. Upgraded to v5.0 on my Raspberry Pi 3B without issue. I was interested in the new group management features, but I also see the Group Assignment column disappear from the Blacklist/Whitelist page as described above. Clearing browser history restores it temporarily, but it disappears again. Tested on Chrome and Edge on Windows 10.
What I think I've figured out, is that we shouldn't expect to see Group Assignment on the Whitelist or Blacklist pages. Rather, it should only show up under Group Management/Clients, Domains, or Adlists.
I didn't realize that the screen shots in the example for Blacklisting and Whitelisting here: (https://docs.pi-hole.net/database/gravity/example/) were not from the old Whitelist or Blacklist pages, but rather from the new Group Management/Domain page.