Reminded me of Stallman's approach a little :D (I fully get why this would be necessary with slack, low bandwidth hotel/train wifi etc make the desktop app basically unusable here in the UK whilst travelling). https://stallman.org/stallman-computing.html
Replaying the recorded code under either rr or UndoDB would have revealed that something odd was going on in the CPU when the recording replayed differently depending on whether HT was enabled. Obviously finding this would have required that the tester replayed the recording multiple times with and without HT enabled