Connection drops out randomly (but consistently)

[#1]

So for the past 6-12 months or so maybe once or twice a month I have a problem with my connection.
When it starts the internet will completely drop out for about 1-2 mins and then reconnect.
It will then consistently do the same every 30 minutes or so for several hours (or longer).
Then it will go back to normal and be fine and 100% stable for weeks at a time.

Outside of this I do notice the same happen more frequently in the early hours of the morning (1-4 A.M.) but still not that often.

I've tried contacting through live chat when it starts happening to check if it's during a maintenance period or if it's on Plusnet's end but always get told it isn't and to check my own router/line/connection.
I don't see how it can be on my end though, if it was then I would be having the problem all the time and wouldn't get long periods of a perfectly stable connection?

It's very frustrating and hard to sort out because it's not a persistent problem.
By the time I get around to trying to figure out what's wrong it's already resolved itself and then there's a random amount of time before the problem strikes again.

I've searched the forum and found several people who seem to be having similar problems, some suggesting it could be a DNS problem. Is there anyone who can help or suggest what I can do to start figuring this out?

I had the problem strike last night, and again this evening and I'm getting very angry and frustrated about it.
I play online games and for most it's a necessity to have a stable connection, and when this starts happening it's restricts me from playing those games because I just can't trust the connection will hold...

For Plusnet people trying to help, my username is gpstudios.
We only every sometimes restart the router when this starts happening and it doesn't automatically reconnect within a few minutes, so any dropouts shown on your connection graphs are from this problem.

[#2]

I just talked with someone on the live chat who showed me some connection logs which are quite illuminating.
He suggested that it's likely something in or around the property that is causing interference and causing the dropouts.

But we have zero idea of anything that would correlate to the times of dropouts.
Can anyone who has had similar problems suggest things we can look into and figure this out?

Thanks.

See attached image for an enlarged look at the detail of the dropouts.

[#3]

I had a similar but worse problem - erratic but frequent disconnections. BT attempted various things but nothing worked for long. Eventually I realised that it mainly happened when it had been raining, and suggested that there might be damp getting into a connection somewhere. Lo and behold, the engineer looked at the junction box on the outside wall and realised it was an old, non-watertight version - no doubt good enough for a phone line with the occasional crackle. He switched it for a modern one and since then it has been mostly fine (one or two disconnections but they didn't 'feel' the same). So it may be worth looking at the physical infrastructure - they tend to focus on the electronic tests, but sometimes eyeballs are better.

[#4]

I've seen so many different things over the years causing dropout, a few that spring to mind are:

Security lights, microwaves, an old CRT TV, Pendolino train, central heating, along with many other things.

The disconnections seem to be clustered in specific hour long blocks, mostly up to around 7am. It could be REIN or similar, maybe streetlights coming on?