It's an issue that, while the mainboard is involved, happens to occur on (at least) the 3 best-selling mainboard vendors compatible with that family of CPUs, at stock settings, so that you can take an affected CPU, swap it through a selection of the most popular mainboards compatible with said CPU and see the same kind of instability problems.

I don't think it's unreasonable to call that Intel's problem, maybe not in terms of culpability (but truly, nobody cares) but definitely in the sense this is doing damage to their brand. If the mainboards are all out of spec then they need to talk about this publicly, rein them in, start a certification program, whatever. Being publicly completely fine with this as long as it results in good review scores but then starting to go "well actually..." when there's stability issues on a small fraction of sold units is not a good look.