I've been having this issue for the past 2, almost 3 weeks.
I am able to use the internet normally for 5 minutes, followed by extremely slow internet for 5 minutes, in a cyclical pattern.
I found out about PingPlotter and decided to give it a try.
I have been pinging several websites that are frequently used and here are some of the results.

From what I have read, hops 1, 2, and 3 indicate the connection between my laptop and the ISP, correct? Since it appears the root of the problem is between hops 3 and 4, am I right to assume that the problem is with the ISP, rather on my side?

Additional Info:
I am using optic fibre. All the lights on the ONT and router are normal. My ISP has sent me a new router, which I have installed. The ONT has also been replaced, however the problem remains.

Any help is greatly appreciated. As someone who works at home half the time, not having a stable internet connection is a huge hindrance.