Please consider having the following JSON for LLD:

[
   {
       "{#TYPE}": "A",
       "{#VALUE}": "test"
   },
   {
       "{#TYPE}": "B",
       "{#VALUE}": "test"
   }
]

You can look at this as at two sets of objects (objects A and objects B), each having a value test:

• A.test
• B.test

There are two item prototypes assigned to this LLD rule:

• trap.A{#VALUE}
• trap.B{#VALUE}

Both prototypes have their Discover properties set to "No". At this point, this configuration will not discover any items, so I add overrides:

• TypeA

  Filter: {#TYPE} mathes A
  Operations: Item prototype contains trap.A
  Discover: Yes
  

• TypeB

  Filter: {#TYPE} mathes B
  Operations: Item prototype contains trap.B
  Discover: Yes
  

All 2 items are discovered, but one of them is lost right away and I have an error about item duplicates on discovery.

This in fact duplicates the ZBX-18551, so feel free to check this task as well.