Threads no drop after some time

[qlwik]

My ZP: 5.17.2.0
I start template, that I used before and it was fine 100%, probably after update I run it as usually, lets say 80 threads, zp use all 80 threads like it should,
but after some time (few hours?) threads drop to 4 and don't rise even if there is execution count -1
my cpu ram is fine it has 24 cores and 72gb ram,

 

[qlwik]

Alright, probably got a reason:
In my template there are (among others) 2 blocks, random number 0-20 and block if random number is 7, then finish template, otherwise continue. I add it to randomly reset instances from time to time, because without it they stuck after some time. In older versions it was working like it should, instances was restarted from time to time and new instances started to work. Now I get problem mentioned in first post. If I remove 2 block problem doesn't seem to show, but I'm afraid that instances after some time will stuck.

Why this problem might occur in newer versions?