Hi there Chris and welcome
The only way to really know is to eliminate all causes, though from what you describe, it appears to be congestion.
Whats the make and model of your internet router?
Power off the router and leave it for 10 minutes,
Then power it on so it restarts then check if you still get the issue.
I am going to opt out of working with you Chris as I feel your better suited for another expert.
You do not need to do anything, you will be contacted when a new expert takes over your case.