I think this is the post you were thinking of:
So…while the latest version of thread established a vendor-neutral standard for thread border routers, theoretically making it possible for any thread certified device to join any existing thread network, it turns out that they didn’t require a standardization of the security method of locking the keys that let you join a network. And different platforms are using different security methods.That explains why people are reporting different results depending on which matter controller they start from. And why people are seeing multiple thread networks where, theoretically, there ought to be only one. The following is a very good explainer on this issue: @Automated_House
Basically right now where you start, can make a big difference, and in particular, if you add a device using an android phone, you need to continue to use android to add it to a different matter controller, and the same is true for iOS. Otherwise, they have a hard time sharing the security key. I don’t know if that applies in this case, though.