Is it an ISP provided router? They're usually terrible I always use my own.

However it depends on the type on internet as well. Fiber tends to be quite stable but when I was on copper lines my internet was up and down all the time with speeds dropping to unusable levels. Then I'd open a support ticket, some engineer would fix it, a few weeks later back to the same problem.

My moneys in the router it usually is most of the time. Although you'll have to check your ISP supports it.

Does it happen when wired and wireless or just wireless?