Overwatch is the only game that does this. My ping will hover around ~65-ish normally (when I’m on wifi), but with Overwatch, it is this constant cycle. Literally rises from 65 to ~125 over a second or two, then goes back down, then back up again. It’s very steady but I have absolutely no idea what’s causing it.
This generally points to an issue between your hardware and the Blizzard servers. Since they are not reporting any difficulties at this time, it’s likely along your route to Blizzard. Please note that other connections to different games may be working with no ping issues. To get a more direct answer, you’ll need to follow the connection troubleshooting guides and post a WinMTR.