Can't locate music on iPhone XS max and iPod

I hope someone out in apple community can help me. I've been having a problem with mostly iPod, now with iPhone.

I'll start off the problem happen when I bought my Mac book pro in June (yea that long ago). In June I transferred my music over the the new computer. Since then I've been getting an error code ! can't locate music in iTunes. All the music is from 22 June 2018 is giving me problems. I've just about replaced most of the music. Now that needs to be replaced also.

Anyone have an idea the solve this problem.

I've contacted apple support they were no help.

Oh PLEASE someone help me.

Melissa 1961