Burning ground issue (0 damage)

I am a mercenary using explosive grenade to ignite oil grenade to create burning ground. I noticed there are specific scenarios where the burning ground do 0 damage.

I believe the burning ground issue i found happens when the original oil patch that started burning from an ignite spreads its ignite to other oil patches - but for some reason the ignite timer is based on the original patch. it isnt refreshing when the new patch is ignited.
so you can get to about the 3rd or 4th patch and it visually burns, but does no damage.
which is a problem, because if you're fighting a boss and you try to put new oil patches if they get ignited by the 0 damage patch they cant be re-ignited with a higher damage ignite. That is definitely a bug because the mechanics of the game are supposed to have strong ignites overriding weak ignites.

This situation basically zeros out my burning ground damage against bosses based on limited space to fight them, because the majority of the boss fight area ends up being on fire with 0 damage burning ground.

I have tested this many times - It does not have to do with my flammability magnitude or fire penetration.

Thank you for your time.