The longest that Swim's hypo rxns even bother to run for is right around 3-4 hrs.
Swim is not an expert on hypo rxns and could bee wrong but maybee it is something as simple as a hypo concentration issue?
Too much water or not enough hypo? Did all of the iodine clear?
Swim had similar problems with Phosacid and narrowed it down to pill gakk.
Maybee concentrate any remaining hypo a little further, add a little more of this hypo that has not yet been diluted with any water, raise the temp a little and let it go for a few more hrs? Swim always dreams of doing this (just in case) and it always seems to remedy the problem.
Quantity of hypo, concentration of hypo, temp, excess water or pill gakk.
Not that I recommend you do this, but after a PM with another bee, Swim has always wondered if NaCl could bee used to "dehydrate" an overly diluted rxn to release gas HI from the fluid? Would this work to clear up any remaining iodine and bring a rxn to completion?