The problem

I run Mathematica 12 from home via a Win11 VM on Proxmox. This configuration has run fine for years. Recently during an upgrade to Win11 25H2 I went to test to make sure everything was functional with a quick BenchmarkReport[] but it caused the kernel to die at Test 3, FFT. Its a very repeatable failure.

Just before upgrading to 25H2 I had changed my processor type for this VM to x86-64-v3 +aes from -v2 + aes. I had issues on another vm where Win11 didnt want to upgrade with v2. I didnt originally run the processor as "host" as I am running dual E5-2699v4 Xeons, Win11 doesnt support by age despite having all the instructions needed.

I have used this VM with Win10 and Win11 for years running Mathematica without issue. In the past I would use BenchmarkReport[] as a quick check of functionality after any upgrades or changes. This is the first time its failed.

A quick test using ParallelTable[sin[x],{x,0,pi,10^-6}] works fine

A quick test of Fourier[{1, 1, 2, 2, 1, 1, 0, 0}] works fine

But a simple,

Needs["Benchmark`"]
BenchmarkReport[]

Fails while calculating Step 3, FFT. The kernel simply die with no error message or warning. If I watch carefully with Task Manager it looks like the kernel dies, Mathematica recreates the kernel, then it dies again immediately.

I also tried running this command through mathscript with -verbose but it gives me no additional details why its dying.

I went back and tested some older notebooks I had. One of the first ones I tried died during a NonLinearModelFit of a PieceWise function with Sin[]s.

Piecewise[{
  {
   y0 + (
     A1 Sin[ 2 \[Pi] ( x - x1)/t1] Sin[ 2 \[Pi] ( x - x2)/t2]
     ) + A3 Sin[2 \[Pi] (x - x3)/t3],
   x >= xon
   },
  {y0, x < xon}
  }]

This had worked in the past but now it dies just like BenchmarkReport, the kernel dies with no errors.

Fixes tried

So, I set the cpu back to v2 + aes for the vm config in proxmox but the kernel still dies.

Set the cpu to Host in case its an issue with AES being passed correctly but it still dies

I had Ballooning memory on so I turned it off, no change

I had NUMA on so I turned it off, no change

I uninstalled, reinstalled Mathematica 12.0 but it still fails

I installed a demo copy of Mathematica 14.3, BenchmarkReport[] and my notebook run without issue.

System Info

Running a network version of Mathematica 12.0 with MathLM on another VM for the license. License is for 2 instances and 16 kernels.

The VM is running under proxmox 8.4.14. The vm was just recently upgraded to Win11 25H2 but I am not sure when I last ran BenchmarkReport[]. I have run BenchmarkReport[] on this vm multiple times with some older flavors of win11 but I cant remember when I last ran it.

I had recently installed the virtio drivers for this vm on the previous Win11 version but I hadnt run Mathematica since then. Could be a contributing factor.

Proxmox has gone through a recent upgrade with a reboot of the host. I hadnt tried test Mathematica afterwards. Could be a contributing factor.

The vm has been tested with cpu set to Host, x86-64-v2+aes, x86-64-v3+aes, numa on and off, ballooning on and off, with 32GB memory configured for the vm. This vm is set to get 2 processors of 8 cores each,

The vm is only running microsoft virtual graphic drivers and is only accessed via remote desktop, not SPICE.

As far as I can tell Win11 is working as expected. I am considering a fresh install of Win11 if no better ideas surface.

The host system is dual E5-2699 v4 with 512GB. The host system runs a mix of vms and containers.

Summary

I know this is probably a very weird edge case of using a VM with such an old version of Mathematica. The kernel dying does seem to fail for more than just Benchmark so its most likely not a single package responsible. The failure is limited to Mathematica 12 as far as I can tell.
Just wanted to figure this our before I start embarking on a bunch of calculations.

Any thoughts are appreciated.