Finisher damage bizarrely low

[Melles64]

I've noticed that I have been dealing incredibly low damage with finishers recently, dealing basically no damage at all in Steel Path and very low numbers on more normal content. Occasionally it suddenly deals a more expected amount of damage and kills the target, but other times I've seen less than 2,000 damage with a crit on a pretty standard level 60 Grineer. This is quite frustrating when using things like Inaros' Dessicate to try and get some health back with finishers, or trying to trigger the Skiajati.

*EDIT* Okay, I'm feeling a bit sheepish, I think part of it was today I forgot I did a riven challenge involving an Extinguished Dragon Key, which is definitely part of the the problem, however the Steel Path run was from another evening so I am sure that is different. The damage is still highly variable, and regular swings even with the key on seemed to deal more damage.