Every attempt to /give to give the player an enchanted item fail. All other tags work correctly. For example:
/give @s minecraft:diamond_sword{ench:[

]}
does not apply fire aspect and instead gives the item in the image provided. The tooltip shows there is a tag applied, but as far as I can tell it has no effect. Relogging has no effect.

This command worked in 18w20c. Furthermore, using the command listed above in 18w21b and then switching to 18w20c would cause the enchantment to appear on the previously enchant-less item. Upon returning to 18w21b the enchantment remained applied.