I have studied these creatures for a long time across multiple tanks. This is probably one of the most debated topics.
Very high flow will cause them to lose their bubbles. This I have found to be true nearly 100% of the time. I don't think its a problem but I prefer them with bubbles.
Too high of light will also cause it. Attached are some photos of some different experiments I have done with different bubble tips, if anyone has questions feel free to ask. I have had thousands of them over the years.
This ones in my profile picture are from a different tank. I do not feed my nems.
So they just get leftovers from fish food etc??? I feed mine a shrimp 1 time per week and the devour it in seconds. Seem hungry to me. Extremely open and happy after the meal!!