I have an A7RV in a Nauticam underwater housing with a Canon 8-15mm Fisheye f/2.8 lens and Sigma MC-11 adapter and an Under Water Technics strobe trigger. The set up has a 1-2 second shutter lag. The camera is set on “Release” and not “focus” in continuous drive mode. How do I fix this? This does not occur with a Sony lens. UW-technics say there is no feedback data in manual mode and that the trigger is not precipitating the problem. I have updated the Sigma adapter firmware and there is no firmware update for the Canon lens. 

Interesting. I experience a lag too when shooting some A-Mounts on my E cameras. I've pretty much stopped using them when speed is an issue. I just assumed it has to do with the adapter interpreting and translating communications between the two.  

Have you tried just the camera/adapter/lens combination to see if it persists without the UTS trigger?

Yes, there is no problem if the trigger is not connected to the hotshoe 

Sorry I can't help, maybe someone knows, I hope you get it sorted!