My iTunes playlists are mixed up or missing.

Recently I upgraded to Mojave. Everything was going fine but recently iTunes started to mix my playlists and folders as well as lose them totally. I have a backup hard drive and iTunes operates from that hard drive. There are three strange things happening and they might be related. First, when I opened a new (not smart) playlist and added songs there, I couldn't add more songs afterward. Second, iTunes started to upload to iCloud but my library is huge so it never really finished that process and I shut down the computer many times in the middle. Third, my songs got mixed and lost as well as my folders and playlists.

I would be glad if somebody could give me a hint about all that's happening.

Thank you in advance :)