High ping response times every 1990 seconds

Hello,

I have RB951G-2HnD and I was using RouterOS 6.6 for half a year. In June I upgraded it to release 6.13, then to 6.15 and now to 6.17.
In all these releases I see something strange which was not present in 6.6.
I am using a program to ping the router, the gateways of my two ISPs and some other hosts to which I usually have 0-1 ms response times.
Every 33m10s (1990 sec) I get a response time around 10 ms for all these hosts including the router itself. My ping graphs look like a comb.
Obviously there is something scheduled that runs at this interval and causes these high response times.
I would like to know how to identify it and if there is a way to fix this. This must have been introduced between releases 6.6 and 6.13.

Regards,
cpg