I'm an amateur using 64bit Kdevelop 5.4.2 on Windows. I found a solution to a problem and post it here for others to find.

When the Git Plugin Under Settings->Configure KDevelop->Plugins and Github-Provider and KDE-Provider Plugins are enabled the Git Plugin is disabled automatically when changes are applied. When disabling Github-Provider and KDE-Provider Plugins the Git Plugin can be enabled but doesn't work or show up at all and is disabled automatically when KDevelop is restarted. It is never listed under Help->Loaded Plugins. I have Git installed.

I fixed this by updating Git to the latest version. It's possible my previous Git version wasn't added to the PATH. Does KDevelop on Windows log why loading a plugin failed? I could not find a log.

This is probably logged to the standard debug output. You should be able to look at that with DebugView or a similar tool.