Fr4nKB My Nothing Ear (2) are now about one and a half year old and they are still glued together, even though I both buds got dropped a few times, twice even on concrete. I even clean them frequently with Isopropyl alcohol, which might even be a possible solvent for the glue, but both buds are still good. So I also would say this isn’t a guaranteed issue which dooms every unit right from the start.
However if you hop over to Reddit, almost not a week passes without somebody sharing photos of their just unglued Nothing Ear bud. Maybe it sort of is a manufacturing issue with some units got bad or not enough glue. Could also be related to the typical environment, for example in hot and humid places this issue might be more likely than in rather dry places.