FS spell ''Cleansing mist'' has a few quirks. I haven't managed to see a pattern with the inconsistencies. Sometimes doesn't heal 2x2 units, especially when only partly in the AoE. Once (only once so far) skipped a whole turn until it healed.
The AOE indicator for the spell is AOE 4 but the effect is AOE 3 (as stated in the description), I already reported it. Never had it skip a turn