This has happened more than once.
I cried when I meditated on forgiveness. Not the part when I forgave others. I started crying when I silently asked others for forgiveness, and even harder when guided to forgive myself.
Once was at the beginning of class, not sure why.
Another time, I remember clearly, I was in a high lunge near the front of a very busy class. The tears just came and they didn't stop until it was time to leave. The teacher said to the whole class, "it's OK if you're feeling grief right now".
Once I cried because I hurt my back doing chaturanga.
The first time I did self-compassion meditation, I cried. "May I be happy" - it was so hard for me to say.
I see you, my student. You're crying in yoga class.
Don't apologize. I'm not judging you. Let your throat swell and your tears fall.
Release. Don't resist your emotions.
This is a safe space.