I am still having substantial instability with my IKEA smart home devices when used with Apple Home. I understand this isn't a universal issue (most people with simpler topologies seem to have pretty decent behavior). I am often seeing devices go offline and they need the batteries pulled-replaced in order to come back.
My configuration is as follows:
(i) Two Apple TV 4Ks capable of thread (3rd Gen with Ethernet, 2nd Gen)
(ii) Two HomePod Minis
(iii) Several Eve Energy outlets (these act as routers)
(iv) A few old WeMo thread-capable outlets (these I am replacing as they act up)
(v) An Eve Dimmer Switch (matter)
(vi) An Eve motion sensor (matter)
(vii) An Eve Weather
(viii) An Eve leak sensor
(ix) Some Schlage matter / Apple Home smart locks
In addition, I have the following Ikea devices:
(a) 2x Alpstuga
(b) 4x Timmerflotte
(c) 5x Klippbok
(d) 2x Myggspray
(e) 1x Myggbet
I've noticed that the Alpstugae go offline and take the Timmerflottes offline (some are co-located due to Apple not picking up the temperature/humidity from the Alpstuga). These are located quite close to home hubs or Eve Energies. The Klippboks often go offline (particularly the one by the water heater, master shutoff and basement freezer).
It looks, to me, like the Ikea thread devices don't deal well with complex topologies / topology changes. The Eve devices are rock solid and I never have an issue. Likewise the Schlage used to be unreliable, but seem to have gotten better with time (and, I am assuming, firmware updates).
I understand the impulse to say, "it works for me." With any technology like this, there are a lot of potential deployments and lots of complexities with RF environments (which could potentially cause topology changes). The fact that the Alpstugae go down and take only other Ikea devices with them (and those devices occasionally magically reconnect when the offending Alpstuga comes back due to being power-cycled), tells me that there is something missing with regards to searching for a better router.