I just wanted to post this out there somewhere because I haven’t found any good documentation on it. In order for me to get both hosted and PSGallery proxy repos to work in Nexus, I had to make sure to include the -ScriptSourceLocation flag, and point it to the same location as -Source. It seems like more recent versions of the PowerShellGet modules won’t search for scripts in the source location for me without specifying script source location.
I hope someone finds it helpful.