The bug
Only one player can access a shulker box at a time. Does not affect any other type of storage such as ender chest or ordinary chest.
No problems in previous snapshots or versions that I am aware of.
MC-171561
Only one player can access shulker box at a time
Resolved
Fixed
9
Apparently this is a reappearance of MC-107427 which has been fixed in snapshot 16w39b.