This sounds like a rather backhanded compliment. 🤔 If you wish to compliment somebody why use negative formulas?

It's a positive comment meaning that you don't disappoint.

Basically, if you tried to disappoint them, you'd likely fail. Thus, you always please them with your content. It's a very good comment.

It means you do not manage to disappoint , so it's a positive comment albeit written very badly. They should have written " you never disappoint.:)

It sounds like a joking way of complimenting you--or a small mistake by a non-native speaker who meant to say "You never disappoint." A very common way of paying a compliment, among US speakers of English, is to say something "never disappoints." This is always a compliment. It is praise for reliability. It is praise for always doing a good job. It is praise for setting a consistent high standard. "Restaurant X is sometimes great, sometimes not; but Restaurant Y never disappoints."