How to trace why an unexpected termination of the script occurs?

Question

PHP

Good evening, colleagues!
There is an IM on 1C-Bitrix, with a fairly large assortment and a bloated database.
When placing an order, the work of the script is interrupted all the time in different places, there is no way to track a clear reason, while there are no errors, the page is simply given with status 200.
I want to note that the script, on average, works out about 1 minute, loading on the processor clearance 100%
All php and apache limits are set almost to the maximum.
There is some suspicion that the restrictions on the hoster's side on the CPU load.
Dear, I ask for advice on how to dig, MB what logs can be collected, I can hardly understand anything in nix.
PS: please do not offer to change Bitrix to a normal system, it's too late...

Answer 1

Enable logging (php-error, php-slow, mysql-slow, nginx-error, apache-error), study, fix.

Answer 2

Hosting is needed with a normal, qualified, adequate technical support.
It is better to give them a ticket to analyze the situation.