That’s because the strategy for target farming in Monos relies on juggling Vessels of Chaos and Vessels of Memory. You need to only clear the good rewards (as far as possible) then hit a Vessel of Chaos for all uncompleted echoes to reroll into better rewards and increase the Unique ones you need. Then, when you have enough good rewards, you hit Vessel of Memory and it lets you re-do all node you have completed already.
You can check a more detailed guide for target-farming here:
