After having a rock stable system for many weeks the BI server started to act up again resulting in frequent system freezes without any hint or trace of what happened.
I have checked the version of the video driver I used and noticed the "prevent update policy" is still working and the driver is at the right version (even after several updates).
Most of the crashes happened overnight or in my absence and since there was no information in the event logs or crash dumps I was totally in the dark...until last week.
BI server locked up twice and I noticed a message that "Windows Defender completed a full scan and did not find any threads".
When I installed BI I have manually created the exceptions for the related directories so I know it is not scanning the BI directories.
I now have temporarily disabled the Windows Defender Services such as real-time scan and and the BI server is up for 4+ days without any issues. Not sure if this is leading me to solution of the very frustrating problem but for now is just too much coincidence for me.
I'll post my updates and findings here. Fingers crossed.