1 It seem the summoned additional boulder on crit (especially, using 3 points, 100%) can critical hit.
So it can continue falling until non-crit hit.
This cause performance issue.
2 The boulder summoned by crit can link enemies.
I believe this is bug because it says “drop another boulder at the same location”
I think these are easy to check by single cast Avalanche.
Or please check below link.