A concurrent issue pertaining to locking block replacement is checking to ensure that they properly fit in the individual gun-and that applies to both how they nest in the barrel lug AND how the wings index within the slide slots where they move vertically, under pressure during the slide reciprocation process. Improperly fitted replacement locking blocks can fail at an accelerated rate. Add indifferent/non-existent lubrication and recoil spring replacement, and you've got the potential for a perfect failure storm-and that's before delving into the intrinsic quality (or lack thereof) of the 3rd party locking blocks.
This is probably even more of an issue with military M9 locking blocks, due to the very unfortunate excessive component replacement intervals, despite manufacturer specifications and recommendations-there is likely going do be more wear, and more wear imparted on the slide rails, meaning that a replacement block with perfectly symmetrical wings will need to have the wings carefully reconfigured so that they match the slide rails' accumulated wear.
I suspect that the odds of that proper locking block analysis and fitting happening are somewhere within the range of "slim" to "none" given the apparent state of military M9 care and maintenance at pretty much every level.
Best, Jon