Humidity
Orin (2018) in Breeding the Vampire and other Crabs (Brachyura and Anomura in Captivity) Husbandry, Reproduction, Biology and Diversity claims that a lidded enclosure with high humidity and little ventilation "can kill them within days" so he prefers not to use lids (p. 116). It is important to note that Orin attributes this rapid death to stagnat and poorly oxygenatexd tanks. And even more important to note is that Orin's standard set up is the most basic immaginable with a sponge for land sitting in a water feature with no live plants, except for occasionally some moss.
This author has found no such susceptibility to high moistre or high humidity using static water features in a heavily planted vivarium with minimal ventilation and a relative humidity in the 90's. Orin's adversion to and repeated belief in his books that heavilty decorated and planted tanks are only for the keepers benefit or aesthetics and all that Geosesarma need or should have is an unobstructed simple sponge-land area, maybe with moss, and a water feature compared to planted vivaria to cycle air with places for the crabs to burrow and hide show that he did not consider that plants in a planted tank can give off sufficient oxygen to prevent the tank from becoming stagant and that he did not consider how Geosesarma have been documented to live in nature. Perhaps for him with his standard bare minimum sponge-land set ups and little new oxygen from plants was his problem all along, with the addition he was working with mainly wildcaught adults, and not that high humidity or limited ventilation kills them as a hard rule-of-thumb.
Not many animals thrive on poorly oxygenated enclosures but this author has done experiments in heavily planted vivaria even with zero ventilation and most would belief that these set ups cannot last long term or be suitable for hardly any animal life, but they have not found that to be the case. The author even has one completely sealed ventilation 45gal vivarium that a colony of isopods has lived happily without outside ventilation for over a year producing mancae and thriving. Eventhough there is no ventilation the use of many plants helps create an ecosystem where the air does not become stagnant. This author does not reccomend at this time keeping Geosesarma like this until they have had the change to test this type of set up out before making any judgements or reccomendations one way or another.
References:
McMonigle, O. (2018). Breeding the Vampire and Other Crabs (Brachyura and Anomura in Captivity) Husbandry, Reproduction, Biology and Diversity. Coachwhip Publications.