Problems with playlists

I finally decided to move from Spotify to Apple Music, mainly because of Spotify's terrible local file management and it getting worse update by update.

So, I bought an Apple Music membership and immediately wanted to move all my playlists from Spotify to Apple Music. I used Soundiiz webapp with this process – it wasn't a perfect solution but the app got about three quarters of songs right. I added the rest of the stuff (all local files, songs missing from Apple music and songs that Soundiiz got wrong) to the playlists manually in Apple Music. After hours of work, I finally got a few of my most important playlists ready.

However, it was quite a shock to notice that today most of the songs from the new playlists in Apple Music have lost by now – it seems that only the local files already in the library (from my computer) are left in the playlists. So, this raises a few questions:

1. What did I do wrong? Why did all those added songs from Apple Music disappear but the local files didn't? I guess it has something to do with the file syncing but I really don't know – at least I want to avoid this happening next time.

2. Is there any way restore the lost songs to my playlists?

3. The third question is about moving playlists from Spotify to Apple Music in general. As I said, I used Soundiiz with the process. It was okay although the app identified some of the songs totally wrong and these songs were quite difficult to spot. Are there any better solutions to the converting process? My playlists are mainly compiled of quite rare and unknown songs which makes it more difficult, I guess.

4. Related to the previous question, there are also local files included in my Spotify playlists. Is there any way to include these songs in the conversion process? Now I had to add all these local files manually.