What is wrong with the remenant data core mission?

No it only shows up in that mission (detail thing) where it says you have some amount out of 9. I have gotten remnant data cores and they show up in my inventory but not on that mission thing. It's one of those things that drives me insane even though it isn't a big deal.

After looking at my current playthrough, where I have just finished the eos vault:

I have one data core listed in the quest,
and six data cores in inventory.

Since this discrepancy is pretty large, and the six is already two thirds the number required for the quest, I believe that the data cores found random stashes are supposed to be something else entirely. Not the quest data cores.
Though both are in fact the same and used for crafting the heleus armour parts. This use as crafting part may be why there are so many found in stashes, that do not count to the quest given items.

There is nothing wrong with that mission. The data cores for that mission are found in vaults and when defeating architects. They have nothing to do with the inventory ones you can get in random loot drops.