UE4 editor is quite stable, but I have found it a good practice to upgrade to next version only after the 1st hotfix, e.g. 4.18.1. Upgrades also come together with code changes, sometimes it is tricky to follow, fortunately the forum is full of helpful professional programmers. I don't use too much blueprint scripts, but I have heard there could also be issues...
he fbx importing works fine, but the UE4 export feature is removed from Mixamo. as a consequence a user made a script for free that solves the problem