I really do think you are having overlap issues. When you went bid for a few cycles and came back to tid...your numbers settled down...for a few cycles. I am thinking that is because the overlap had cleared. Now it appears you are back in that cycle of overlap.
I think I would try bid for a few days and see what happens. Cass is on such a low dose, that any residual insulin going into the next cycle is conterproductive. I might be wrong----but, I really think that is what is happening.
It makes sense to me, that a kitty that is getting micro dosing tid, would struggle with overlap. The doses are so small, that anything left is negative. Where with a cat like Kitty that is on almost 4 units tid....overlap is Good! She can use all that is left.
I really would consider trying bid again.