Thanks, Isaac. I'm testing in Safari 15.6 on Mac OS 12.5 (Monterey), but we're getting reports from users, most of whom use Windows (and probably Edge or Chrome.)

When I test in Chrome, it seems to work as expected. So, the problem appears to be browser-related wrt how it processes Javascript.

No, we're not running through a pre-caching DNS

Our server is fairly quick. Top shows plenty of reserve capacity.

Code
top - 20:46:23 up 35 days, 18:16,  1 user,  load average: 0.05, 0.09, 0.07
Tasks: 235 total,   1 running, 234 sleeping,   0 stopped,   0 zombie
%Cpu(s):  0.8 us,  0.2 sy,  0.0 ni, 99.0 id,  0.0 wa,  0.0 hi,  0.0 si,  0.0 st
KiB Mem : 16223096 total,   453496 free,  1424980 used, 14344620 buff/cache
KiB Swap:  4095996 total,  3989244 free,   106752 used. 13658204 avail Mem

The Stovebolt Geek
https://www.stovebolt.com/ubbthreads/ubbthreads.php

Server Information
UBB.threads Version 8.0.0
Release 20240826
Server OS Linux
Server Load 0.11
Web Server Apache/2.4.37
PHP Version 8.3.11
MYSQL Version 8.0.39
Database Size 1.82 GB