Upon reformat of High Sierra, iTunes duplicates many of my tracks.

I have my iTunes folder on another hard drive. When I reformat, I'll open iTunes and change the path to the folder on the other hard drive. I'll then close iTunes and then hold the "option" key. A window asking me to specify the path appears and once I specify, all of the artists load automatically.

Unfortunately, many tracks will duplicate themselves once I log in to iTunes Match. Last install, I went through and deleted all the duplicates and I thought all would be well. Strangely, it seems the same tracks duplicate each time. There are over 500 and each time, they are with specific albums.

I also set "Devices" to prevent from syncing automatically. I put a tick into the box that says "Keep iTunes Media folder organized" and "Copy files to iTunes Media folder when adding to library".

I'm at a loss on how to stop this from happening again. Quite frustrating. It is probably something I'm doing to myself but I'd like to know how to permanently fix this.

Thanks.