I can sympathise with your situation, having one
M2P of four which consistently requests updates for incompatible firmware and consistently fails to update in the manor you describe, the other three are fine and I have no issues with those.
Not having the original pro I cannot give advice from any direct experience with a Mavic Pro but I can tell you the steps I took after months of failure with my
MP2. (I was eventually successful).
I had 'Assistant 2 for Mavic' and the original 'Assistant 2' I don't know which one you should use for the Mavic Pro but for the
M2P you should use 'Assistant 2 for Mavic' but I was having no joy with this with failures as you have described.
I downloaded the original 'Assistant 2' and found it has a Factory reset option.
I tried a factory reset and downgrade to the earliest firmware on the list. It failed.
Did a factory reset and tried 'Assistant 2 for Mavic' got the inconsistent firmware message and update failed at 22%.
and again; and again. etc.
Frustrated I tried a factory reset again but still no success.
I remembered reading somewhere that it was recommended that you should first update the controller and secondly the drone, tried that but no success.
I am not sure why I did this or why it worked but it did. I connected the controller to the PC simultaneously with the Mavic.(both switched off.)
I ran 'Assistant 2 for Mavic' and switched on the controller and refreshed the firmware to the latest. Success with the controller.
I left it switched on and also switched on the drone. I ran the update for the drone which now bounced straight passed the 22% to 40% .... 93%; 95% update failed.
Ok still no success but it is now failing differently than before.
Went back to the correct procedure trying to update using 'Assistant 2 for Mavic' inconsistent firmware and failure at 95%.
On about the third attempt the message changed to Flyzones need updating. Did the update and finished with success and the green tick.
Switched the drone off.
Switched the drone on and all was well.
Switched battery and tried 'Assistant 2 for Mavic' got the inconsistent firmware message again but eventually after several fails and restarts it did update 100% and the green tick.
The moral of this tale is Do not give up just keep trying.
I still occasionally have trouble with just this one drone but being patient and trying again and again so far has worked. All four are currently up to date.