Fps drops see here; https://www.reddit.com/r/GlobalOffensive/comments/6mldl4/found_a_fix_for_anyone_that_may_be_experiencing/
Other reasons for fps drops could be heat & throttle related so monitor temps for both cpu and gpu with hwinfo64 - if you use this app, don't enable the sensor it warns you about it could cause instability with this particular sensor, it will be the first thing hwinfo will warn you about and will advise not to enable.
Game bar/ Xbox dvr recording could be an issue in some games. Game bar's fullscreen optimisations can be an issue in some games. To disable fullscreen opt the setting is under the compatibility tab for the game's exe, or you could create a shortcut and the option will be there also.
So theres...