I just replaced upper and lower body shell and a LR motor arm after a crash - and I've been doing evaluation flights.
Which arm was this prop on?
Have you checked that the each arm sits symmetrically with its right/left partners?
I crash a
Mavic 2 and one front arm drooped, it turns out that a spigot protrudes from the top of the front arm pivot. For the drooping arm this spigot was bent on the and was forcing the arm to droop.
Also there is a plastic thrust washer ( black ) that sits on top of the arm, presumably to keep a gap between the top of the arm and the drones body, does the MPP have the same arrangement and did you have any spare washers left over at the end of the rebuild. With regards to the spigot, the MPP front arms appear to have the same arrangement, did you notice if the spigots were bent. BTW if you position the arm at the tipping point between spring-open and spring-shut the front arm pivots are probably very easy to remove and refit.
With regards to the rear arms I can't find a dismantling video that shows a clear shot of the naked end of a rear arm and I appreciate that the design of the MPP and
Mavic 2 differ wrt the rear arm pivots but ..... On the
Mavic 2 there is a travel limiting lug on the inner end of the arm's male-half of the pivot, it moves in a circumferential groove in the inner end of the female-half of the pivot. This lug seems prone to being broken off and that allows the arm to rotate when in the flying position. Since it appears that the female-halves of the rear arm pivots can be bought separately from the arms I would guess the male and female halves of the rear arm pivots can be separated. If so it might be any idea to check if there should such a lug and if so if it is present on both arms.
BTW, with the
Mavic 2 when fitting the arm's male-half of the pivot into the female-half the lug slides in an axial groove in the bore of the female, meaning the arm has to be in a certain position to fit it and remove it, from memory this was the fully closed/ storage position.
If the MPP's rear arms have a similar lug there is probably as similar position requirement.