Well I finally got back to the shop and took my bike in with the pedals still attached. Showed him the play in the pedals. He tried tightening them up (which I had already) done, and agreed that there was something wrong. Ended up swapping them for a different brand, so I’ll see how these go.
I did neglect to tell them that I have ridden through water that completely covered my foot (and subsequently, the pedal), but I thought of that after I swapped the pedals over.