Hello!
Mikrotik Model CCR1036-8G-2S+
A couple of months ago, periodic freezes (packet losses) began to appear on the network. I began to look into the problem and saw that the load on one core (cpu23) jumped around 20-80% and often reached 100% for a long time. Moreover, the total processor load is 1-3%.
I started looking for the reason for loading the kernel. I found out that it is being loaded by Firewall. Naturally, the first thing I did was check DNS queries. Everything is fine there. As a result, I discovered that if I opened the tab IP - Firewall - Connections, the kernel load dropped sharply (to 7-20%) and remained that way. As soon as I switched from this tab to another, after a while the load on this kernel again increased to 100%. Including almost immediately after rebooting the router. By the way, after a reboot the problem arose again on the same kernel. The firmware was like 7.12.1.
I couldn’t find the cause of the problem and left it until the new firmware was released. Until this time, I launched WinBox on one of the servers and opened this tab there. We worked like this for about a month, and then we updated the Mikrotik firmware to version 7.13.5.
At first everything worked without problems. In any case, we did not notice any obvious problems with network freezes. But after about 2-3 weeks we again discovered problems with loading the processor core. Now there is a similar problem on cpu3.
However, I have not yet tried to reboot the router (it is very difficult to find a time when they will give the go-ahead to reboot it). But even if this helps, based on experience, it will not last for more than a month. It’s easier to open the tab IP - Firewall - Connections again on one of the servers and wait for the new firmware.
Has anyone encountered such a problem? Can you recommend anything to solve it?

Addition:
April 1, 2024 7:30 am rebooted mikrotik. The load on the cores has become uniform. A day has passed and it seems that the load on one of the processor cores is starting to increase. Now on cpu10 the load remains at 15-35%. At its peak up to 53%. I'm watching further.

Addition № 2:
3 April 2024 14:25. The load on one of the processor cores continues to increase. At the moment, cpu10 load is on average 43-73%. At its peak it reaches 90%. Total CPU usage is only 2-6%