Hmm...
Theory No.1 is a no go since the SH3 sea bed is as flat as the surface in a shiny, 0wind day. The only thing changing its shape would be the uboat.
Theory No.2 is somewhat acceptable since you were in the middle of a minefield. Note that the mines have the bad habit to spawn out of the bottom rather than being dropped by surface ships.
My personal theory and the most reasonable i suppose is that the
Catafark is somehow involved to this mystery. I dont know how or when but i just know it is that! 