I'm making a model for a Unity game. I have the model finished, as well as the Texture & Lightmap UVs on separate copies of the model from another program (Headus UVLayout). I just need to apply both UVs to one copy of the model to be imported into Unity. However, the new UV is a spaghetti mess. I've done this dozens of times before with no issues. Images below.
Both copies of the model require 2 UVs, so one can be overwritten with the other
The final result has always been one model with two accurate UVs, one being the texture UV and the other being the lightmap UV. But now it results in a mess that doesn't even look like both UVs combined.
Am I doing something stupid? I've double checked the process and I'm not seeing anything different from how it's always been done.