I have also experienced this to some degree. Upgraded to 4.22 and it seems that the engine constantly dips below 15 fps in intervals. It seems to be still trying to render everything even while behind other windows, which I don’t think it used to. Usually, entering another menu/blueprint menu would be more smooth, but it’s just as slow as the main viewport while this is happening. It seems to happen more when the engine is trying to load/unload large files into RAM, so maybe it’s something to do with the transfer process. Not really an answer, just confirmation that someone else has had this issue.