Github can be horribly slow sometimes (tested from different machines and through different ISPs) and difficult to tell if that is down to the framework used to render the pages or any other parts of the system.

A few years ago it started a transition to react. It has been less snappy ever since to me.

Agree, the new code viewer is horrid. Also breaks right-click navigation between files for no reason. Not once have I triggered the interactive editor mode on purpose, but happens all the time accidentally, trying to select / hightlight a line. So frustrating…