These issues are common.
My whole village suffers exactly the same issue irrespective of the ISP. The reason is Openreach, they own and operate the copper and some of the infrastructure.
I setup monitoring equipment across the village and the drops are random. These issues also cause slow upload speeds which is also a massive issue with TCP as timeouts occur resulting in more requests and more problems.
Every time Openreach gave me an excuse I modified the monitoring equipment based on RaspberryPi’s to account for there latest excuse at the end, i even included radio’s to monitor for radio frequency interference of which we had none.
The only solution was to get a FTTP line which solved the copper issue.
The real issue is that openreach unlike the ISP’s are not regulated, you cannot complain to anyone so there is no watchdog able to impose fines are get openreach to solve the issues. We need central gov to create a body that actually regulates all of the connection not just the bit that is customer facing. For some of us the ISP does not provide the copper and some of the infrastructure so its irrelevant which one you choose.
At the time of my faults, I wrote to my local MP and he did nothing. He even lived in the village so presumably had the same issues as the rest of us mortals.
Complaining to the ISP only eventually gets you to the point where they release you from contract early which is actually your right given that the service cannot be provided. You change to another ISP that is regulated but you still use the same first mile infrastructure so the issue is still there.