1
You indicate you have Bitdefender installed, open Bitdefender and check in that apps settings to see if it is set to scan your system on startup, that may be causing the problem.
2
Otherwise, check to see if your PC is producing any small Watchdog dump files, I will check those to see if they provide any insight into a potential cause of the system crashes.
Open Windows File Explorer.
Navigate to C:\Windows\LiveKernelReports
If there are any Watchdog dump files in the sub-folders of that folder, copy the files onto your Desktop, then zip those up.
Upload the zip file to the Cloud (OneDrive... etc.), then choose to share those and get a share link.
Then post the link here to the zip file, so I can take a look for you.