C pigpio timer inaccuracy on raspbery pi 4 with raspian

[nhunder]

Hello there,
I am using the pigpio C library and tried to figure out what accuracy the timerfunctionality has with the following code:

the output of the code looks something like this with everything in microseconds:

625
375
0
250
500
375
376
624
250
375
500
375
625
500
125
500
125
750
375
250
625
500
375
251
624
500
375
125
250
375
500
250
375
375
250
250
0
375
750
750
500
750

does anybody know where this inaccuracy n*125us for every timer interrupt come from.
i aasume it has something to do with kernel and the interrupt priority of the timerinterrupt, because i noticed under heavy load of the OS the inaccuracy becomes bigger.

And do you know if there is a possibility to get a more reliant timer with this library?