I have the problem in the heading.
When using my 5DSR and EOS utility 3 to remote shoot, I can have either the live view, or I can fire the flash (Studio flashes - PixaPro 400s).
My "workaround" is to use liveview to compose, then close the window and take the shot.
I'm pretty sure this used to work though.
TIA, in advance.
I never use EOS3 for Live View shooting, but I have read that shooting tethered with Live View disables Linked Shooting which is I believe the feature you are asking about. Many Canon flashes allow you to release the shutter when tethered in Live View.
I'm looking for documentation. Hopefully someoen who shoots with this regularly will respond.