Cracked forcing cones, flame cut topstraps, they have happened. The model 19 forcing cone has a relief cut that most other guns don't have, and troubles became noticeable (above the statistical average failure rate).
Shooting large amounts of the 125gr JHP ammo was becoming the common practice and since guns were failing at a higher rate than before, (and nothing else had really changed) the hot 125s got the blame.
S&W didn't design a K frame .357, exactly, they took a K frame and adapted it to the .357 Magnum. When you do something like that, there are limitations.
Things worked pretty well for a long time, giving officers am easier pistol to carry, day in and day out, and still able to use .357 Magnum ammo when required. "Practice with .38s and save the .357 for serious use" was the mantra for many years.
Trouble is, when you run your engine at "war emergency overboost" too long, bad things tend to happen.
The Model 19 is a fine gun, but its not a .357 mag in the sense an N frame is. Not even close.
Also, note that a number of guns came out of S&W with problems after Bangor Punta took over. When they stopped pinning the barrels, more than a few guns wound up going back to S&W for repairs.
A friend got an 8 3/8" M629. Nice gun, except after a few hundred rounds, the barrel started to unscrew. This was in the early 80s, with an unpinned gun. The barrel was noticeably canted. Gun went back to S&W. Came back a few weeks later, barrel straight, and S&W saying "nothing wrong".
If you don't have a need, or a want to shoot .357 Magnum at the levels it began at, the model 19 is a pretty good gun. If you do want original full .357 Mag power, the 19 is NOT the gun to do it in.