I and my crew are incredibly frustrated with the fact that sometimes the treasure bugs out and simply cannot be picked up. When this happens you can partially fill the pickup interaction, but about a quarter of the way into the interaction/pickup it stops. We have tried picking it up from different angles and we've tried giving each crewmember a chance to try and pick it up. Sometimes looking at it from another angle, letting someone else try to pick it up or burying it (if on an island) and digging it up again fixes the problem, but much more often we just end up leaving the treasure due to these methods not always working.
This seems to only happen with treasures that are sitting on top of/against another surface (be it underwater, on an island, on a rowboat or on a ship). For example, we might find some random crate on an island, but we'll be unable to pick it up. Or we'll be unable to pick something up which we dug up from a treasure map. Or we might find something flush against the deck of a shipwreck (such as in the captain's cabin), and then be unable to pick it up (recently this happened with a Chest of a Thousand Grogs and with some crates).