After applying dots, the addon seems to just permanently suggest drain soul

Ah, I'm leveling and don't have shadow embrace, so most likely it's trying to cast drain soul to stack shadow embrace but since I don't have the passive, it's just permanently looping to try and get the stacks buty can't.

Does this sound like it could be the issue?

That's absolutely the issue. The addon tries to build SE stacks. Since you can't, it doesn't know what to do.