Why do I have duplicate songs...ALL the time?

I just did a sync from my Mac mini to my iPhone 7 and cannot understand the iCloud duplicate songs on my iPhone. The steps I took to sync were to download my iTunes library (onto Mac mini) and that was fine, not duplicates, no iCloud symbols. I then synced my iPhone with the Mac mini and said yes (on iPhone 7) to erasing current content on iPhone and yes to merging content. After syncing...my iPhone 7 library looks exactly the same as it did before the sync, meaning duplicate songs with iCloud symbols and the same song no iCloud symbol? I am really confused about iCloud and how it seems to relate differently to each device. Please is there anyone who can shed light onto this situation of duplicates on devices not being updated? Thanks so much for your insight.