Server Load Limit
If you see this in an actual MyBB page then the limit isn’t actually reached, its in the script.
[ edit inc/settings.php, – ‘load’. Change the value to 0 here, then login and change it again in the ACP.
ACP > Configuration > Server and Optimization settings > *NIX Load Limiting > edit this. ]
(hmm it’s already zero so made a copy of settings.php and used the copy instead.. Holistic troubleshooting.)