This past Saturday I repotted my Crown of Thorns, and today (Wednesday), I realized that several lower leaves were yellowing, and it seems to be spreading higher and higher. The pot it was in was too tiny at this point, and it really needed new soil. It's cactus/succulent mix, cut with perlite. I watered lightly on Monday, no fertilizer.

I had an earlier bud blast issue I posted about when I first got this plant, and it ended up being too little water. It still happens here and there (you can see one failed bud in the photo, while the rest have bloomed), but not as bad as before. I thought perhaps the larger pot might and fresh soil might resolve that issue as well. Instead I get yellow, dropping leaves.

What's going on?