Hello @walter!
You bring up a great point- and from my own tarot experiences I can agree, decks really do have their own personalities! 
Since you mentioned that your deck has been pretty on point up to now- my first suggestion is that it may be time to cleanse your deck. Old readings and natural energy can accumulate, muddying up readings and giving your cards a distracted feel. If you haven’t cleaned the cards in a while- now may be a good time! 
If you have recently cleansed the deck, then there may be another issue at play here. The cards may be mirroring your own mind. If a question is not clear to the deck, it makes sense that the answer will also lack clarity. Perhaps meditate with your cards and really focus the question at hand for a few minutes before beginning the reading 
My third and final tip is something I have to constantly remind myself- the deck may know more about a situation than we do! Even if the cards drawn seem completely irrelevant- it is good to question if maybe it is actually our interpretation that is off. As we see in @Amethyst’s lovely tarot haikus- one card can have a host of readings: some traditional and many personal. An “off-reading” could be a good opportunity to look up the card and explore alternative ways to read it 
It is wonderful to hear you are enjoying the deck- The Green Witch Tarot sounds lovely! Hopefully you can get to the bottom of the moody mystery and get back to on point readings soon 
Good luck and blessed be! 