Mantis 2.25.6 (with patch 0032086) in connection with php 8.1.16 can lead to high delay for setup of initial screen, i.e.
Call mantis page --> delay until initial list of issues is shown (anonymous access is enabled, similar to mantisbt.org's site)

However, the delay is reproducability not seen when using mantis 2.25.6 with php 7.4.21.

The problem appears to depend on browser cache history. I.e., switching between mantis 2.25.6 with php 7.4.21 and mantis 2.25.6 with php 8.1.16 seems to trigger the problem, according to the state the 7.4.21 session is left at.

I've added screenshot of strg-shift-e in firefox.

Notes:
a) I've also seen the problem
Login with authenticated user --> delay after initial page (view issues in my case) is setup

But this is obviously harder to reproduce, couldn't catch a strg-shift-e for that yet

b)
In case there is access to external data in the internet this would be prohibited by a firewall. So this /could/ account for the delay.