Quote Originally Posted by pushin_tin View Post
There is a display limit of 30 debuff icons per mob. If you apply dots on a mob that already has, say, 40 debuffs, your dots will apply, but you will not see them. There is a hard limit of 60 debuffs that can be applied to a mob. This means if there are already 60 debuffs on a mob, and you apply dots, they will not work.

GG Diadem SMNs.
This. But based on the info you gave, it's probably this.

Quote Originally Posted by hagare View Post
I think it has something to do with how many debuffs and DoTs can be on a boss at the same time.
Also some skills with the same effect overwrites the old ones.
like NINs and WARs slashing debuff.
You use Dancing edge solo. It works all good. You use it in a raid environment, someone else's dancing edge or storm's eye will make your icon disappear. Similarly for all defense down buffs. As for DoTs? This doesn't happen (i.e. they disappear) and it's likely that the icons were not there in the first place. The DoTs are there and ticking though. You can test by using fester when you don't see all 3 DoTs displayed, but you applied them. If you still got the 300 potency fester, then you hit the display limit. If you didn't, then you hit the debuff maximum.