Spark causing instance crashes?

Twice in a row now, I've been going through the Church Dungeon level 2, encountered a high resistance Sin Lord, started spamming my Spark+Fork skill into his face, and about halfway through killing him, the instance crashed, disconnecting me. Can't be coincidence if it happens twice in a row in different instances, but I've got no idea what is the culprit.

It could be Spark AI crashing after too many projectiles being thrown in a very tight area. It could be something completely different. I don't know.