I imagine with this what is happening is that the matchmaker wouldn't put you in the lane/match it gave you with the character you have at high priority. It does try to balance lanes in terms of skill and has modifiers for heroes on your mmr. So this may not be the matchmaker not seeing you'd...
Even if you have Cancel Ability Mode set to Ability Key, McGinnis wall Erupting will ALWAYS use the underlying keybind you have set to Cancel Ability (even though it's not visible in that mode and shouldn't do anything).
The damage stack does increase from both of the refreshed bombs.
What you're seeing is that the second one's damage is calculated from before the first bomb's damage stack has been added. The added damage a Bebop bomb has is computed when it is cast, not when it explodes - but the total stacks...
With replays, the issue can normally be fixed by browsing to a different match than that desired and then going back to the match you want and downloading it.