I have a Fluke 28-II Ex from 2017 with the same issue.
When I remove the AAA holder from the battery compartment and place AA batteries it is solved.
No modification is needed. Behind the AAA assembly there seems to be a kind of extruded round plastic shape to hold AA batteries as well.
Perhaps the 3m drop test cannot pass anymore now, since the AA batteries are not so strongly hold as the AAA batteries in the "reducer" assembly.