From what I have read here, ACV is not the only thing that people relapse from after discontinuing. That seems to be a common complaint when folks go off antifungal meds and/or probiotics. I think it means the system is not yet healthy enough to keep things in check on its own, for whatever reason.
I think what is being overlooked is the absence of friendly bacteria in the gut, which is mostly the reason we get candida overgrowth in the first place. When treating candidiasis, or yeast overgrowth, it is very important to repopulate the gut with bacteria using probiotics. This will help prevent a relapse. If a relapse occurs after stopping probiotics perhaps it was stopped too soon. Probiotics alone takes a very long time to overcome a candida/yeast infestation. I have been through this many times, but once learning about essential bacteria in the gut that keeps candida under control, I have had success in recovering from it.