Reed basket was showing 16 Inventory Slots instead of 8. Was playing on 1.16 rc.4 hosting multiplayer for myself and 2 friends on an ad hoc server. Friends looking in the basket saw the correct 8 inventory slots, when I looked inside it displayed 16, but it did not let me store more than the 8 slots could hold.
Edit: When I picked up and placed the basket it appeared normal, but when my friend looked in it the same glitch happened, he could see 16 slots instead of 8. Seems like the person who places it sees it correctly but it's glitched for others.