FPS drops can be caused by bugs or inefficient coding in games, or by hardware problems. It is worth doing some testing to see if your computer/hardware is the source of the issue, hardware problems don't evenly effect all games.

Common hardware issues are CPU, GPU Overheating and being thermally throttled and or Insufficient memory.

Please show your current system performance by running a quick 3DMARK Time Spy benchmark using Default settings, and post results link. Example : https://www.3dmark.com/spy/11775405

Your first run details, system hardware, clock frequency's and average temperature will provide an accurate baseline,.. thus any advice, adjustments made can be quickly tested with another Time Spy run to compare your results.