Sorry to see this happen on your figures, Luisenigma1 and Platty. The warning is much appreciated as well.
Apparently HT's still using the fragile rubber printing over the stretch suits. I'm a museum poser as well, and this happened to my The Amazing Spider-man 1 figure's armpits, so I gave him an arms-spread-wide stance. Learned since then so I had my MoS on the same stance, and now my Armored Batman figure.
There is some damage under the left arm of my BvS Supes. I've never had any of these figures in a super dynamic pose but I do keep the arms close to their sides. How do you make Superman and Batman look good in an arms wide stance? They'll take up a lot more room that way to.