Do you use MSI Afterburner / RivaTuner? I had the same issue after Roblox updated to 64-bit and introduced the Byfron Anticheat.
If you use Afterburner
-Go to your taskbar, and click on the show hidden icons button (left of time display)
-Right click on 
and click “Show”
-In the bottom left, click on the “Add” button and go to this folder path:
C:\Users\ username \AppData\Local\Roblox\Versions
-Go through the folders until you find “RobloxPlayerBeta.exe”
-Open it, and select it in the list of applications (by default it will be under Global)
-In the menu change “Application detection level” to “None”
Your issue should be fixed, very specific fix for this program though so lmk if you don’t use this