Revan Bugged for us Last night.
From my googlefu it seems that if you bring revan Below 10% hp while he is doing a channeled spell (force storm/lightning/falling rocks) it bugs.
we died, reset him stopped dps @ 11% and brought him under 10% after his channelling had stopped, worked fine.
so perhaps its something similar for hardmode, perhaps just dont dps when channelling is happening :/