On a behavior pack, if more than one custom entity has the minecraft:economy_trade_table component with a specified table path, only one of them will work, the other(s) one(s) will show an empty trade window.

Reproduction steps:

1: download the world file attached. This world has 4 custom entities and 4 custom trades

2: Interact with each custom entities, only one entity is showing a trade

3: delete the entity with the working trade from the behavior and relaunch the game

4: Interact again with the entities left, one of the entities that hadn't trades before now have its own trade available

5: (optional) Repeat the last 3 steps and see the same result