I had something like 350 Hero Seals yesterday night, and only 150 left this morning… I didn't purchase anything, so what happened?

The only notable thing since last night is my hero levelling to 21, followed by a message about an Empire's Glory attire, which seemed to be given out with the level – I would not have bought it, that's pretty sure.

Is there a possibility that I misclicked something? Another common error I could have made? Or is it really a bug?

(Is there a way to have something like a log of my hero's actions and transactions, so as to check by myself?)