Mi router 3g speed problem

Hello everyone, I have a mi router 3g ( 4 core and 256 ram version). I upgraded my internet package to 500 down / 50 upload after this almost every two hour my speed drops to 5-10 down, if I replug my cat cable from this router or restart my original modem (not this router) ıt's working normally but this happening almost every 2-3 hour. I read this topic " So you have 500Mbps-1Gbps fiber and need a router READ THIS FIRST" but in my situation my router has 4 core and I'm not using Sqm. I only installed samba4 package and tranmission for seeding.

There's no straight line between more cores and better performance.

Install htop, what does it say about the CPU load?

I don't now how to use htop and I couldn't find information about it. But below you can see cpu load from statistic package

I reset my router and now I'm currently using without any packages but my problem continue.