My understanding is that chip QA at Intel took somewhat of a nosedive post Haswell. From my ignorant but interested outsider perspective, everything from Broadwell on seemed to be a mess execution-wise compared to Haswell (modulo TSX), and _especially_ compared to Ivy Bridge.

Some of the recorded comments on https://danluu.com/cpu-bugs/ (First update section) mesh with my observations, but I wouldn't know enough to tell if I was on to something, or just confirming my own biases.