I know this sounds very strange, but I also don't know what it is.
In my map, I have a built in deep sea diver helmet concept, which gives you night vision and water breathing when you're inside water and wearing a pumpkin. This concept strangely works on my computer, but not on others'. I know this isn't a bug you usually see here, but I don't get it either. If needed, I can send the map file with explanations on how to activate this.
Commands:
(Repeating command block) scoreboard players set @a dsdh 0

(Chain command block powered by previous command block) scoreboard players set @a dsdh 1 {Inventory:[{id:"minecraft:pumpkin",Slot:103b,tag:{display:

}}]}

(Repeating command block) execute @a[score_dsdh_min=1] ~ ~ ~ detect ~ ~1 ~ water -1 effect @a night_vision 6000 1 true

(Chain command block powered by previous command block) execute @a[score_dsdh_min=1] ~ ~ ~ detect ~ ~1 ~ air -1 effect @a night_vision 0 1 true

(Repeating command block) execute @a[score_dsdh_min=1] ~ ~ ~ detect ~ ~1 ~ water -1 effect @a water_breathing 6000 1 true

(Chain command block powered by previous command block) execute @a[score_dsdh_min=1] ~ ~ ~ detect ~ ~1 ~ air -1 effect @a water_breathing 0 1 true