I keep getting two matching bruises towards the lower/inner part of my rear delts. It's happened three different times now, spread out over a year or so.
Could this be from back training? I haven't changed anything, I'm going a little bit heavier because I'm stronger than I was the year before last. If not from back training, I don't have the slightest idea? Nothing is hitting/pushing on my back there that I'm aware of?

Fairly purple, and kind of oval shaped.
As far as I know I'm using pretty good/strict form.