Back again!
So I escalated the matter to the guys here - Its a visual issue. It is as I suspected. The subs do indeed happen on the server so that's why everything is in fact written down in the match report but the animation engine bugs out while rendering. :/
So I was told that it's on the task list with the devs.

Oh btw, I do wonder if resetting the game or jumping to the home-screen and back to the match, after the bug occurs, would refresh the animation engine... I haven't experienced this so I've never tested it out. If you guys have this issue again can I ask that you try this out? At least the jump to home and back to the match thing.