Interesting. Thanks for giving some insight!
I don't mean to sound rude, and perhaps it's not something you're willing to answer, but don't you have some unit testing for individual cards? Obviously, it would be unrealistic to have unit tests that cover all the possible interaction of cards in the game, but I would have assumed you had some unit tests for the basic use cases of a card... like "if you sacrifice a saproling to Thallid Omnivore, the life total goes up by 2". Then your phone rings and someone goes "Ben, I don't know what you did, but the unit tests on Thallid Omnivore don't pass anymore!"
Again, there are going to be bugs when it comes to weird interactions, but it always surprises me when the "base case" of a card doesn't work properly.