The thing is, it's not just a single bug as often.
For instance a bug about xp loss after host migration was fixed, except it still happens sometimes.
There's also the bug where you don't have mods on your mech weapon after host migration, which only affects affinity indirectly.
All things considered, you should xp your mech only if you're having fun with it right now, which I did. Else, you'll have a much smoother experience if you wait.