I’d say this happens to me at least 95% of the time - in my favor or in favor of my opponent - it doesn’t matter.
It used to happen with monostegotops but now I see it mostly happening with Thor (probably because we all have him above 4000 trophies) when we each have the same dino but at a different level.
What happens is - whoever has the higher level dino (and goes first then) lands the hit - and the lower level dino always crits his first hit in response.
So with mono - it would always happen that way with slowing impact. With Thor - it’s always dsi of course.
I can’t ever remember the higher level dino ever critting against the same dino of a lower level, on the first move.