That's exactly what a coincidence is. Rather, a red herring. People self diagnosing problems and deciding this is a solution.
Does it even occur to you that: HomePod mini has no ability for Home hub to be turned off, like Apple TV does, and that this might be for a reason? If there was a critical flaw with HomePod mini's ability to serve as a home hub, don't you think Apple would at least allow it to be turned off?
99% of these issues are people's networks. Period. People think that because one thing works a little better than another that means it must be the thing, not their network. Spoiler: it's always your network.
Happens once or twice, sure we’ll call it a coincidence. But every single time and it becomes a rule. Seems Apple rarely admits to flaws in their software (the new architecture exception… thank goodness they pulled that atrocity). Do you read what’s going on? Many people in many forums having to dance to the devil, going through this whole rigmarole to get their HomeKit to work again, like it did before Apple HomeKit coders got their hands on it in the form of a software update. Unplug all your hubs, then restart your network, then plug in your hubs, then restart your iPhone, then do the Hokey Pokey and turn yourself around. Why is that? Because Apple doesn’t publish any troubleshooting steps to fix their crappy coding and people are having to try to figure it out on their own or wait for the next update. You shouldn’t need to be an MIT graduate with a major in network engineering. If it is my network, then Apple should publish what network settings are needed to make their stuff stable.
When my HomeKit setup is stable on a certain hub for many days, then for no reason, it switches and everything goes down, that’s not a network issue. That’s an Apple algorithm issue. Why they don’t allow us to de-select the HomePod, I have no clue. They don’t allow us to do many things like actually automate a door lock or garage door.
By the way, it’s 100% not my network. Maybe terrible Wi-Fi chip in the HomePod but definitely not my network. I have an eero Pro 6 system with five nodes all with wired back haul. Verizon FiOS Gig up/down. All my eight AppleTVs are hard wired. I have a total of 17 HomePods (OG and Mini mix). When I do speed tests at these HomePod locations, they’re consistent on my iPhone getting expected speeds. Why is the HomePod Mini so awful, I’ve no clue. Maybe outdated Wi-Fi equipment.
So, please, if Apple’s algorithm for switching hubs is flawless, explain to me why HomeKit underperforms when a different hub arbitrarily picks up the duties of active hub. Especially when it was previously working just fine.