So I realized I stupidly made symbol art at the wrong size, needed it for my alliance. But when I deleted it my game became completely unresponsive and froze, though the music continued to play. And on the list it seemed to have disappeared. This screenshot is far as it got, you can see the partly faded but frozen confirmation window. The art I tried to delete was in slot 01. Yeah I don't make much symbol art, I'm here to enjoy the combat
Closing the game manually and restarting shows the slot was not deleted. I have tried this multiple times now and this happens every time.