Unable to fix iTunes library migration issues on MacBook Pro

I am on a Mac Pro running Mojave and iTunes 12. My iTunes library has happily been on an external ("old drive") HDD drive for years. I recently installed a new SSD internal drive and copied my iTunes folder to the new drive. Now, the majority of my albums and songs do not show up or cannot be located. I can add them manually, but there's over 1TB of files. The albums that play normally are in the "Music" folder (Music/iTunes/iTunes Media/Music), but there is also a "iTunes Music" subfolder inside the "Music" folder with several subfolders. iTunes on the new drive does not seem to want to "follow" these folders now, although it worked fine on the old drive. I have directed iTunes to the proper folder on the new drive. Is there a fix for this? Thanks. - Blake

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