Can you share a lot more detail? Request and response body and headers, endpoints, etc. If you can, share code.
In NodeBB 1.18.6 ACP, when I click;
ACP > Dashboards > Logins or Users or Topics
the page URL changes to include one more /forum, additionally, this subfolder doubling "/forum/forum" can be seen in the links on the ACP page: (such as last 30 days/ last 7 days on the image below)
This problem only occurs in Logins/Users/Topics pages, not in "Overview" or "Searches"...