RB3jr Chest shops will have a count of a certain number of things in chest, for example it will say 1 in chest, but when you click on the sign to buy it says, "out of stock" (for me I still had 1 item in the chest, but it could not be bought by my customer) I have had many different players test this on different shops. And I myself have as well, on many different game versions, 1.20.6/1.20.4. 1st example tested by skylexia and I is in /warp emporium -5408 2 -4415 will be the stone shulker boxes 2nd example tested by legxi7622 and I in /warp rb3 -9440 26 -10102, all spawners for sale bugged 3rd example tested by khronesgehrig and I /warp everything -8270 66 -6387, all spawners for sale bugged 4th example tested by rb3jr /warp spawner -4104 28 14387, all spawners for sale bugged 5th example tested by legxi7622 rb3jr /warp dirt -1147 64 3202, all shulkers for sale bugged 6th example tested by legxi7622 properx /warp rb3 -9411 26 -10172, all head shops for sale are bugged The issue is that chests have items in them, but they give a "shop is out of stock!" though its not. During testing we had found that most blocks /items still are working, player heads, spawners, shulker boxes full of items, seemed to be the only problems. All chests tested with different game versions including 1.20.6.
Looks like this is a problem with item data being changed during the update from 1.20.4 to 1.20.6. Nearly all items with any sort of data, spawners, heads, enchanted tools, shulkers and probably others. All these items will have changed data based on the update changes. This means that the shop signs made in 1.20.4 for items with nbt data will no longer work. The solution is simple, if not annoying. You must remake the shop signs. I tested it with taddors shulker stone shop at -5408 2 -4415 and found the shop works fine with the same shulkers but the sign that has been remade. His shop won't work because he needs to remake the sign, but I tested with the shulkers of stone on a new shop and it works fine. I also notice you have re-made the signs at /warp rb3 -9440 26 -10102 since this bug report and those appear to be working fine now.