I don’t think it’s so much a risk of immunity as a risk of fatiguing your body too greatly to the point that you feel really unwell, making the diet feel very undoable, and also affecting your weight loss as well. When you take a longer break, you give your body time to get back to homeostasis and normalcy so that when you begin your new round, your body is fresh and ready for another go. To me, that is one very main purposes of Phase 3.
So while I understand the thought process of “well if I don’t want to stay at this weight, I should skip P3 and just keep going” (or take a super short break) – this often ends up backfiring.
Here are a few posts to help you decide:
Extended hCG Rounds and Shorter Breaks – positive experiences with these
I hope that helps!