My wife has exactly the same problem - no shop lists items. player shops works fine.
We have already deleted Documents\EA Games\Ultima Online Stygian Abyss\User Data\ACCOUNTNAME\SHARD and even the complete User Data folder, even without success.
Also PincosUI deleted and reinstalled, without success.
My account on her PC has the same problem.
If I can provide any debugging information, let me know how, and I will provide it.
Edit: I found some logs in the directory of the EC Client, it says the same thing everywhere - I added one to this post.
[18/06/20][20:31:41] <string>: [string "UserInterface/Pinco's UI/Source/System/Shopkeeper/Shopkeeper.lua"]:319: attempt to index field 'currentShop' (a nil value)