Yeah this looks like the typical issues with UMT when importing non Undertale games heh. The tool is built targeting proper decompilation of both Undertale and Deltarune but has wide support indeed for many GMS games, now some may fail to import...
they need to have a strong line up on the launch titles too. I think they should move metroid prime 4 to the next console because by now it has been quite a while and there's no release date scheduled yet