Additional Unique Item from strongbox - no drop

I spent trans,aug + regal on a strong box. It had a modifier for an additional unique item to drop, so I put 3 more exalted orbs on it. Chest popped, no unique dropped at all... Is this supposed to happen? In POE1, additional unique meant you were guranteed 1 unqiue from that chest.

You aren't guaranteed a unique drop, if one had dropped you would likely have gotten a second.

If and Likely????? Its a modifier, it should be guaranteed to happen. Completely pointless IMHO. Disappointing. Its bad enough that 90% of the unique's are un-useable past level 50. Thanks for the reply.

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Mummbles#1717 wrote:

You aren't guaranteed a unique drop, if one had dropped you would likely have gotten a second.

Doesn't work like that in PoE1.