Instability with x86_64_v3 builds for Gaudi Allen tests

There appears to be a new instability in some of the Gaudi Allen tests in Moore, where some counters in the x86_64_v3 slots are fluctuating build to build.

Take for instance todays 2024 patches build

https://lhcb-nightlies.web.cern.ch/nightly/lhcb-2024-patches/31/

See the diffs in both the dd4hep and DetDesc x86_64_v3 builds.

This morning, I created !3414 (closed) which contains ref updates based on the above nightlies build, and ran this ci test

https://lhcb-nightlies.web.cern.ch//nightly/lhcb-2024-patches-mr/381/

If you compare that to the nightlies, you will see the counters flip flopping around.

It looks like something related either to the PV finding, or the velo tracking.

I am not 100% sure when this started, but the first I can see in the available history is here

https://lhcb-nightlies.web.cern.ch/nightly/lhcb-2024-patches/19/

@raaij @cagapopo Any ideas where this might be coming from ?

@rmatev FYI