Project Stutter, is Github addon related?

I have been working on a Unity2D project, and it's been running fine. However, I took a hiatus of a few months whilst out of country and returned to continue working on it. I had to update to 2018.2.17f1 and also added the Github addon to this version, despite getting a "Login Failed" notification whenever I try to connect via Unity and the "Changes" section actively not updating.

Ever since doing both, the project runs fine for a few minutes, then after a few rounds of action, the game starts to stutter until it's virtually unplayable after about five minutes. Do I need to update methods in the project, is it an issue with Github, or might it be something else? All my other programs run fine on this computer, so I doubt it's a software issue but certainly not ruling that out.