Hows the ventilation on your equipment

Internet issues can be from any link in the chain going to/from the source.

Best way to determine the issue is to go about it scientifically. Take a component out of the system, test. Take another out - test. Including cables. Or, start with the most simple setup and add in a component. If you start simple - computer connected directly to modem via Ethernet - and it has issues right off the bat, you’ll know it’s not your own setup - or, it’s one of the base components.

What graphing software is this?

ping is not suited as a network diagnostic tool. You can not draw any conclusions from a observation.