I know, the explanation is as follows. So far I've seen him giving a 92 hp blow. (at base damage 26-32). But some monsters are a bit too quick or a bit too tough so they have physical resistance. and base damage delivered can be a percentage of a range 26-32. Sometimes it is 20, and sometimes 5. And triple damage chance may fall on this weak blow.
It's no bug, and the only way out is to be really quick. Or swap to a Mace.

Say, my 29-level Druid (Might 93) is Dagger Master (L10) and wields two daggers (2d3+7) and (2d2+5).
He delivers straight damage 26-32 (avg. 29) which becomes 41-47 (avg. 44) when Heroism (at level 7(10)) is cast. with extra 20 hp damage (Fire Aura on both daggers cast at Lev 7M). Let us assume that triple damage are outdone by underdamage chances. But still, it is 60+ damage on average and recovery now is 60-14=46 (L8+6(item))

And if that Druid develops Mace to L10 (expert) and wields a Mace (2d4+11), he delivers damage 32-38 (avg. 35), which becomes 47-53 (avg. 50) when Heroism (at level 7(10)) is cast. with extra 10 hp damage (Fire Aura average damage on 1 weapon cast at Lev 7M). And still, it is 60 hp damage on average and Mace recovery now is 80-14=66 (L8+6(item))
(One more question - is this mace is of increased speed what is means exaclty?)

BUt with mace he is able to wield a shield and have better AC and be hit less frequently.

IMHO at higher levels (20+) Mace + Shield is better than 2 daggers.
But early on, two daggers at Expert level 4 + Fire Aura at (expert 4) + Heroism spell (4Exp) are formidable for weak mosters, while early mace wileding is fatal for a slow and weak Druid beginner.
My thoughts are for a solo fighter druid, not mage druid.

so the out