I've been trying to recreate to get screenshots, but this only happens when you're in battle with a rare pet that has the fire elemental proficiency. After it casts Explosive Fireball and Combusting goes off on your pets, for some reason the enemy pet gains the Combusting status, and subsequently blows itself up. Will provide logs as soon as I chance upon a fire proficiency pet in the wild

Does this happen in the Lost Grove too or only in the Festival Zones?

Both; the first time I saw it was in the Fall Festival Zone, where the themed pet was taking damage every time my pets were, too - I have a screenshot of the logs, but only the very ending tidbit where the themed pet died to its own Combusting. A few days back I saw it happen again in the Lost Grove, when I wasn't running a Fire pet yet, where the enemy got Combusting after it ran out of on my pets. Didn't think to screenshot that one, though...

Hm. Okay, so both in the Festival Zones and in the Lost Grove, the enemies are using the same Explosive Fireball ability. The Combusting Debuff attached to that ability is then what's causing the issue as it's using the player pet version of it.

However, the Lost Grove seems to already have code put in place that checks if it's coming from a friendly or enemy target and then adjusts the code accordingly. The Festival Zone code does not - so I will add that in and that should be fixed now.

If anyone notices this happening again or specifically happening inside the Lost Grove, please let me know and please screenshot the battle log again for me. Thanks. =)