Why is the number of calls to the script falling?

Question

PHP

Hello, I
ran into such a problem:
1) There is a script that is installed on several sites
2) It counts page views
3) I connect the script to another N number of sites.
It turns out the following: on 1 site there were 1k views per day, after increasing the total traffic due to the inclusion of the script by N amount, the traffic should ~ increase by 2 times due to their total, but it turns out that the general one now sees ~ the same as it was, but on 1 site sees traffic now only 500k.
Actually in which direction to dig? I write everything in mysql, there are no errors (too many connection), nginx also does not give errors.
It seems like there is a limit on the number of simultaneous readings of a file, where can I see such errors?