Why is LSAP using a huge amount of memory?

Hi all, 

Just needing a bit of help. My Windows 11 dell inspiron 7591 2in1 (i7) has been having issues with LSAP (lsass.exe) using an inordinate amount of memory. Omce it starts up it just keeps usind more an more memory until the system crashes.

So far I have done;

• a couple of clean installs -  the problem comes back as soon as I unpause auto updates. Unfortunately as windows now wont let you install selective updates I'm not sure which one is causing the problem.
• fill system scan with bit defender for viruses
• ensured my drivers are up to date
• Run a DISM restore heath 
• Run chkdsk
• Turned off BOTH File encryption and Device encryption
• Run sfc /scannow
• Hardware scans with Dell support. 

so far no luck so any pointers would be appreciated. 

Thankyou!!