In the last war, my sumle on attack was on low health and applied burn to the defender. After the War Cleanse Effect the status effect was removed and was not reapplied.
Based on the description of the effect, it should have been reapplied (“as long as low health”).
Just an assumption this happens because the effect is only applied once, when the health treshold has been passed. But based on the special skill, this should be checked every round, even if it is removed.