I have the same issue but the other way around. I got an external SSD, and just bought a new Macbook Pro, where I want to move the whole library to the internal Macbook Pro drive.
I use two SC6000 with an USB stick. First of all, when I open the library with the external SSD, the library’s just empty. I copied everything to the internal drive, empty.
Tried Lexicon, it finds the library, but only transfers the playlists, not the tracks which are also both on the external and internal SSD now. It already shows 0 tracks per playlist. Help