Version 2.8.2 Debian Buster PREEMPT-RT ISO Freezes

I seem to have solved the problem. I've exchanged the PC for another one of the same type and it seems to work fine. Admittedly it's early days, but I've had LinuxCNC running for quite some time without any freezes.

The only obvious difference between the two machines is that the BIOS on the new one provides a pair of Realtek PXE boot options that weren't there before. Perhaps this is a sign of subtle networking differences, and some aspect of the networking on the first machine wasn't compatible with LinuxCNC. Otherwise the two machines appear to be absolutely identical.

Not having a definite explanation for the freezes isn't very satisfying, but I'm very glad that I now have what seems to be a stable system.

Many thanks to those who replied. You've taught me a lot along the way.

andypugh wrote:

I wonder if RTAI is an option? Kernel-mode RTAI won't work, but you can actually run LinuxCNC-uspace on an RTAI kernel.
But you probably have to build your own...

The answer is, sadly, no. 
It looks like it wants to work, but locks the machine solid during the setup phase. 

At this point the machine locked up and auto-rebooted...