iTunes not saving my playlist changes

Hi there,

The last few times I have updated my playlists on my computer (and spent hours on them) they have sometimes reverted back to the unchanged playlists after a few hours and also don't update on my phone. This has happened a number of times over the last 2-3 months and I'm really irritated about it. My computer and phone are on the same WiFi network & I pay for Cloud space.

Thanks