Help with new Canon RP

[Hairy Sea Squirt]

New Canon RP in an Ikelite housing and strobe. I have two dives with it and on the second dive, the images all had a darker area across the lower quarter. It looks as if there was something blocking the strobe light from that area. I moved the strobe around and also have a Sola1200 photo light for focusing. Nothing I did changed the shadow area. Any ideas?

 

[Barmaglot]

What was your shutter speed? I don't own an EOS RP, but a quick Google search shows its flash sync speed to be 1/180s.