The question can't be answered without examining the particular guns referenced, and determining how they'd been assembled at the time the problems occurred. The installation of the torque lock spring in the locking arm ("flag"), and how the bottom end of the spring was secured in the recess within the bolt channel, would have to be examined.

Also, whether either/both of them had ever been disassembled by you (or a previous owner, if you acquired them used) to the point where the hammer and bolt had been removed, or the locking arm allowed to "tip out" and pull on the spring's bottom leg upon removal of the hammer (which could've changed the correct installation, albeit without the owner's knowledge or intention to affect the spring being secure in the frame).

While I did have one of their long time customer service guys (who used to be in production, and now retired for several years) once tell me that for a short while it was wondered if some of the early production revolvers might've had the ILS springs incorrectly installed, he said he hadn't heard of any problems since the early days of it being used. He said he remembered a few problems reported (in-house) with the early ILS-equipped revolvers, but those had been during the development of the X-frame guns (.500/.460), and due to the horrific recoil.

I've talked to someone else from the factory who not only told me of some ILS-equipped revolvers being used by some competitors who racked up high round counts, and without experiencing any "lock failures". He was one of the competitive revolver shooters who used them.

Now, I tend to prefer my S&W revolvers without the extra safety lock, myself, being somewhat of a traditionalist. I only own one of the new model revolvers equipped with the ILS. As an armorer, the ILS-equipped revolvers mean there's 5 additional parts in the gun, but it's not like armorers are told it's suggested to keep extra parts for the ILS on hand. The only thing about the lock system even covered in the class was replacement of the locking arm and torque lock spring, if ever needed, and that was covered in a short few minutes.

In my class I had some armorers from agencies who were longtime revolver guys, and while they didn't care for the aesthetics of the ILS, neither they, nor any other armorers in the class, could think of any instances where a newer model J-frame (still popular as backup and off-duty weapons) had experienced an actual lock-related problem.

One of the guys said he'd fired more than 500 rounds of Magnum ammo through his PD , without any problems, and he was looking forward to ordering a M&P 340 (which was only offered with the ILS at that time). I thought he was probably a bit of a glutton for punishment, myself.

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Ret LE Firearms inst & armorer