Hi Russel,
I've got also some strange effects by using instant replay in Prepar3d 2.5 (with Hotfix). It's nearly the same as you've described. I have also some yellow triangles flickering around. They change colour from yellow to orange-red and then suddenly disappearing after a couple of seconds.
It seams to be a new bug. My previous installation (V2.3) was working fine with instant replays.
Frank