I first noticed this when I fought map 5 MS mini boss with my Omega red. After using the first sp3 the death field stopped working despite the icon showing it to be active.
I then dueled a MS with my 3* Omega red and I faced the same bug. the fight has been recorded here is the link to that fight
https://youtu.be/e-hSsZgcOYMPlus here is the screenshot from the mini boss fight