I can't be the only one
That’s because it has a casting time. There’s no global cooldown really in the game, instead most skills have a casting time (and animation).
This is the same for most of the interrupt skills in the game, though some may be faster than others.
Usually a heal skill will take longer to cast than your Conc shot. It’s all about being able to quickly read what your opponent is doing, and sometimes anticipate their next move
I’ve witnessed this as well but I’m still low level and haven’t needed to interrupt specific skills most of the time so it’s not as annoying.. yet. The bar for casting finishes, I watch the arrow hit the enemy, then a second later the effect is put on the enemy, that’s how it seems anyway.. I would imagine that once the arrow that was shot using the casting time hit, the effect would take place.
I could be wrong though, will check on it later again.