Don't recall seeing any complaint here or in the FB group.

It sounds more like you have tried to e-file MI separately as a state only return after the Federal was transmitted.  It's when that happens that rule 830, which requires MI-8453 to have been signed by the taxpayer(s), would cause the MI return to be rejected based on what I was able to gather from the MI Dept of Treasury website.  If the MI return is e-filed together with the Federal return, MI would accept the Federal e-file authorization automatically.