I had purchased these previously - and ended up returning the box. There was no adhesion going on for closing the envelopes. It might simply be that they were lying around too long in stock.
40%+ of the envelopes in the previous box of these envelopes were not well glued on the sides. Defective envelopes needed to be taped on one side before it was mailed. The current box of these envelopes so far do not have any envelopes with this type of defect.