edit2: Yeah, the more I have thought about it, the more convinced I am that it is related to travelling settings/travelling speed. I would enable every retraction setting that promises to decrease stringing, enable any setting that helps avoiding printed parts when travelling, decrease significantly the travelling speed… But I’m leaving the original comment below just in case.

First of all I would confirm that the printing speed is consistent between the multi piece project and the single one. I get that kind of aligning issue in tall thin pieces in my miniatures if I set the speed too fast… the nozzle scratches the piece slightly and makes it wobble by going too fast, resulting in that effect.

Once you have checked that, I would try to print the single piece but offsetting it to the position of the one in the bottom right of the images, just to discard bed leveling, because that one seems to come out slightly worse than the others.

If the single piece still comes out ok even after being offset to other positions, then my last theory would be that by printing multiple pieces, they are having enough time to cool off individually until each layer gets to them, and the material is not fusing properly. And to test that I would try to print groups that slowly increment in size, first a pair, then 3, then 4… Until you find the amount that doesn’t come up right.

I think those are all the theories I can come up with for this issue, but if I come up with something else I’ll update.

edit: Now that I think about it, another difference is that the single piece wouldn’t have travelling moves… Maybe they are the ones causing this if they are too fast.