With the launch of Ubisoft Connect they altered the system so that units are earned by levelling up - which is done by gathering XP. There is an FAQ available on the Ubisoft Connect website which details how this works.

@j4y10123

I had something similar happen. For me I assumed it was because there was a NPC who was trying to help but not doing much so everytime I tried to open the chest another raider came and went.

To get around this I went for the other chests in the location and came back to that one last. By the time I got there the NPC that was stuck was waiting on me to help open the chest.

The only alternative I can think of would be to reload the game from a recent save (such as autosave).