On a realm, the first stack of arrows to be fired from will often get "stuck" in whatever inventory slot they are in, and cannot be moved to another inventory slot, placed into containers, or stacked with other arrows (except for fired or dropped arrows that are picked up).

If the stack is partial and is the first stack of arrows in the inventory's "pickup order", trading for arrows with a fletcher will cause each trade to fail (no arrows or XP received, and no emeralds given), yet the villager will think each trade was successful and the trade will eventually be exhausted and locked as normal.

Logging out and then back into the realm-or restoring the stack to full by collected fired/dropped arrows-temporarily resolves the issue, but it almost always reoccurs.