... This means Mazda hasn’t figured out what happened to this oil burning issue on these 2021 2.5T’s. ...
Actually, Mazda is talking out of both sides of their mouth in this TSB. First they wrote: 'The root cause of this concern has not been identified yet'; but then immediately follow that up with: 'Since this issue has been reported after a valve stem seal modification, it is very likely that valve stem seal damage is causing oil to leak into the combustion chamber'.
This almost sounds like they changed their mind on what to provide for the reason, and then didn't edit out the original statement. However, it seems likely IMO the information about the stem seals is correct, and this will eventually be flagged as the root cause. I also think Mazda's real problem with this is deciding which repair to make. Same old story - do they trust their stealerships to do the significant engine repair, or are they just going to do the simpler (but probably more costly) engine swap.
Can't help wondering if Mazda is going to start to buckle under the weight of their various major engine issues - the ones we're aware of, and also what may still be yet to come.