This doesn't look like a filter shadow. I'm betting more there is something going on with the rear of the lens that is blocking the light. Check and see if the black guard that is inside the lens mount has come loose or is misaligned somehow. Make sure there isn't something sticking out of the lens preventing the mirror from flipping all the way up. You say this happens with 2 different cameras and I assume doesn't happen with Other lenses.
A filter shadow would likely have an opposite shadow like on the top of the photo or all 4 corners or 2 of them. A Hood misalignment, same thing. A flash shadow would probably be semicircular unless you're using a square hood..