Missing / Grayed out songs - Songs been altered to different versions - HELP =(

Recently tried to synch iphone to iTunes, which I had not done for some time. I have now got apple music.

What happened to me was that some of my own songs (mainly mixes for fitness and dance which would not exist in apple music or iTunes store) have been greyed out.

There are no icons next to them. There is seemingly nothing I can press / no functionality from right click.

They will not play on the PC and vanish from ipod classic when it is synched. They do not play on iphone they are greyed out here too.

The files are still on the computer, in iTunes library - but there are a LOT of them and to have to go through and re-add every one would be very time consuming - and what is to say the same wouldn't happen again?

How can I get these back?

The second problem is that some of the files seem to have been altered by ITunes. e.g. a zumba fitness track has been completely changed to a children's song with a similar name....

Can anyone offer some advice please?

I have tried making sure computer is authorized, toggled applie music / iTunes library on / off to see if it makes a difference...

How can I get my songs back on =( Absolute nightmare.