This problem can be caused due to different factors like faulty graphics drivers, higher graphics settings on low-powered PC, background programs, etc.

The FPS in Roblox games may drop if the power saving mode is enabled on your Desktop or Laptop. Similar to smartphones, the power-saving mode limits the performance of your graphics card and CPU ...

If you’re suffering from software bugs or other problems with your graphics card, one of the first things to try is performing a clean installation of your drivers.