I have the Apache error.log filling with these message (had a full disk this morning), since upgrading from from 5.2 to 5.4 on Debian 10.13.
This installation was first started in NAV 3.x era (2012) and continually upgraded and moved to different hardware a couple of times, so it is very possible there is junk in the configs that is no longer relevant
[Tue Sep 27 08:48:55.649027 2022] [wsgi:error] [pid 541:tid 140035050575616] [remote 127.0.0.1:35090] [Tue Sep 27 08:48:55 2022] [WARNING] [pid=541 nav.web.auth] User default denied access to /tags/tagMultiSeries