Given the paper already appears to have a correction for something minor, one more would seem appropriate, yes - it’s a pretty jarring error.

But it’s just disingenuous to say it affects (let alone “invalidates”) the actual study. And shouldn’t a proper pedant spot that the top pin isn’t even where Lübeck is - that’s Rostock.

Good spot.

Does the swap in the position of the two cities compromise the findings in any way? If not, it's an irrelevant mistake like misspelling a word. What do you expect them to do? retract the paper because they misspelled a word?

It could, because in the timeframe the paper is about, they were geographically near, but had no real direct connection to speak of. Traveling over land along branches of the 'old salt routes' took at least two days, and that was fast. They were transport hubs of different branches of the early Hanseatic League.

[1] https://en.wikipedia.org/wiki/Hanseatic_League

This is not the equivalent of a 'spelling error'.