I read on another forum that the fly more combo case is what causes the problem.   I too was getting the over speed errors on the rear blades, and since I have stopped using the fly more combo case, they have stopped.   I also did investigation using csvview and confirmed the over speed.   Apparently the fly more case can cause the rear blades to move slightly out of correct shape, and hence, not work as effectively as they should.

It's not the case's fault... it's how you store your Mini.

At some point the drone must be kept firmly into position, the case does so through various contact points. The bottom one is quite recessed compared to the blades position but there's still the possibility for the blades to be pinched in between the support and against each other...

My mini sat on the Fly More case for months, did several off-road bicycle trips on my back and yet the blades are in perfect shape. I only loosely tie the blades together to avoid them slipping out of position before the drone si fully seated it.