If the monster gets stunned within the casting of any skills that have skill effects, the skill effect will stuck in animation and will disappear only after the next skill cast. Even dead monster will have that skill effect playing.
How to reproduce:
There are a couple of turtles on a beach outside of Hoddmimis. After some time in combat, they will try to cast a “melee shield”. This skill has a long casting window within which the turtle could be stunned (for example with a “shield strike”. It will result in a canceled and failed skill cast. But the glowing effect will stay until the next cast of the skill (maybe even the one that has the same particles). Even after death, the same effect will stay.