Sorry to hear of your mishaps with your Shields. I don't own the 9mm so I can't comment. I do however have the 45 shield and can't say enough good about it so far.
I don't know your previous shooting experience, I don't know your experience with small light weight semi-autos. Putting if 264 rounds through a small aggressive gripped carry gun and some +P rounds on top of that should pretty much leave anyone with some hand fatigue or pain in my opinion, that is a lot of rounds to put through a full frame target gun!
I know the Hogue makes a nice looking HandAll grip for the Shield that may be a nice aid on both guns for about $10-$12.

I honestly was impressed with how little recoils the 45 transmitted with narrowed grip.

Failures to feed could be from how the bullets were set in the mags, might help to tap them on something firm to set them back tight in the mags. Limp wristing might have contributed to the failure to feed if the slide did not make the appropriate travel cycle.

The Bodyguard sounds like the challenge. I am realizing that compact guns have a narrower latitude for error and seem more sensitive to variations that other guns tend to absorb. They are what they are and with a little learning curve are pretty darn amazing.

I'll give you credit for that endurance of shooting that many rounds with small lightweight guns!
Karl