so not only does this not test the rest of the cpu at all - meaning you can run into problems with other parts of the CPU that aren't stable at those frequencies, because they're not being tested because it's only running the AVX units - but it also doesn't test frequency/power state changes at all, so you can run into situations where as soon as you close prime95 and it drops to a lower p-state, it'll crash.
gpus have run into similar things with furmark and kombuster and other power-virus tests... actually the GPUs themselves will detect when they're running and throttle down, so they no longer even do the thing they're supposed to, but, gpus also change power/frequency states under real-world workloads, just like CPUs, and they don't under furmark/kombuster. this actually caused a crisis at the ampere launch... all the testing had been done with a "pre-release bios" that only allowed these sorts of power/thermal testing, and it turned out that while the chips might be stable at max p-state, they weren't stable when they shifted back to a lower p-state, or from a lower p-state back to maximum. That was the whole "POSCAP vs MLCC" thing.
prime95 and furmark were very very popular 10 years ago but that's where they belong, they don't do the job anymore these days.