It wasn't just pre 29s and could happen on later 29s. But the big factor was the advent of newer, heavier bullets that weren't known or common when the 1st 44 magnums were factory tested. The problems had to do with recoil's affect on moving parts, i.e., momentum. As was posted above, also a weak grip could cause the problem for the same reason a 1911 (or any semi-auto) will mal-function when not held firm enough.
This affected 29s all the way up thru the 29-3, although the majority of 29 shooters never experienced the problem, having not pushed theirs to the limit with super hot loads and/or 300 gr + bullet weights.
But Smith addressed the problem in 1987 when they introduced the 29-3E model with what they called the Endurance Package. It included the new floating hand to eliminate disengagement under heavy recoil thereby preventing the cyl from 'jumping time'. The floating hand was used in other models as well, albeit without any fanfare. There were no real major changes, just a few tweaks actually that addressed the issues heavy shooters experienced. By 1990 one additional small change was made, the cylinder notches were made longer and slightly deeper for improved cyl bolt lock-up.
Although the M24 had long since been deleted as a regular production model by then, these changes did make their way to the M24-4, another special production item as one of "The Twelve Revolvers" distributor exclusives sets, an Ellett Bros. of Chapin, SC special offering. The M24-4 was the "Through The Line" version of those twelve; pg 339 in the SCSW 3rd. The only other M24-4s were a few over-run guns sold thru regular distributors w/o the epitaph engraving or other special embellishments. They are the most durable 44 Specials ever made by S&W, IMO.
That's the situation as I understand it. Others may add to that.
Hope that helps,
