Got a bit of a weird problem going on. Basically, I have used these cheap routers in the past, and you know they worked, but I always wanted to get a Mikrotik for the customization/configuration, etc.
Finally managed to get my hands on one a few months ago.

When I got it, I set it up, all is well. I did not use it to do the pppoe part, only used it as the "second router" in my home network. (all lan traffic goes through this)
So my setup looks like this:
- Modem+Router. 1/1gbps FTTH. Used for wifi, but has the Mikrotik router in DMZ.
-> the Mikrotik rb750gr3
--> clients

I have no exact timeframe, but as time goes on, my ping goes up.
Like, I use these online services, play videogames, that kind of stuff. And let's say, my ping when I do a reboot of the router, I have a ping of 35ms.
Few days later, it crawls up to like 38-39ms. 2-3 weeks later? 45-46ms. It kinda stops there, so the growth is not infinite, but it jumps up quite a bit.

- Have no convoluted/complicated firewall rules. This is a very simple home network.
- The 1gbps is barely ever maxed, it's there because it's cheap and this way no single user can saturate it. Great for work.
- CPU barely goes up to like 3-5% on the router if I check with Winbox.

Let me know if some data is missing, or if I should get you a log or anything.
As a workaround of this issue, I have set a scheduler rule to reboot the router each early morning, and this solved the problem. But I like Mikrotik, and I want to deploy it at job sites, installations we do. However, I cannot risk a constantly ever growing ping, so I would like to find the culprit here. If a 10$ ASUS/TP-Link or any router can manage a constant ping, Mikrotik must be able to do the same as well - it must be some misconfiguration or tiny error somewhere.