Opcache keeps restarting itself

Hi,

Problem: Opcache keeps restarting itself every 30 seconds or so.
My configuration:
Plesk 12.5
php 7.0.14
Apache / Fast CGI

Default settings for opcache, except the memory moved to 128 MB.
opcache.memory_consumption=128

There is NO memory wasted I never reach max memory.
When opcache restarts it leaves no trace in "last restart time" or other restarts:
last_restart_time never
oom_restarts 0
hash_restarts 0
manual_restarts 0

My opcache_hit_rate rate is...

Opcache keeps restarting itself