Ok, go back to that mesh, look down the list of details and look for the one that says UV channel (or something similar), it will be set to 0, you need to set it to 1. Its a quirk of how the generator works that it doesn’t set the lightmap channel to 1 after it creates the channel 1, so you have to do it manually.
As I mentioned before though, the automatic UV algorithm isn’t very good so your lighting will likely still look kind of poor (but it at least won’t give you these errors). Best option is to do the UV Unwrap yourself, as I said there are plenty of tutorials on youtube about how to do that.