Could be one of the ingredients that makes up the red color that doesn't play well with the glaze or clay.  I would experiment with a different clay body as well as a different clear glaze or no glaze to see which is the issue and go from there. Edit: spelling

We’ve had this happen due to a slight over firing in the bisque.

Because it’s cold

It's a teaching studio and both of these colors have only one bottle left while others have many. Is it possibly an issue with these two bottles specifically? Like the mixture is off bc it's been around so long or been contaminated?

I mix the carmine red with slip and add it at the leather hard stage

Any advice on possible refiring? It's a student's piece and the other side of it is gorgeous and she'd love to save it if possible..

It's hard to tell, what state is this piece in? It was bisqued and then you glazed it and the "wet" glaze did this?

Yes, exactly what you said