After double-checking which model I was using for 1.7.2b, (wasn't sure where it was, but I found it) I wasn't using Gemma-4-Sparse-QAT, but the normal Gemma-4-Sparse. I don't know if it was still a reported issue on 1.7.2b, but I'll try it on 1.7.2c and let you know if it happens again.
Thanks for your time.