The shadow orb count is displaying correctly on the Devouring Plague button, but the border never lights up to indicate the presence of the Devouring Plague debuff on the target. I also tried with the spell status inverted and the border never disappears after the spell is cast and the debuff is active.
Thanks!

It think we miss the debuff spell identifier. Could you enable the debugging tooltip and tell us what it is please ?

The spellid of the Devouring Plague disease debuff is 158831