At least I found one consistent reason for songs being cut off:
All my songs that have the cloud status "Waiting" (dotted cloud icon) are cut off, some sooner, some later.
You can easily check if that applies to your songs by:
- display the list of titles
- right-mouse-button (Mac: CTRL-click?) in the labels of the columns and check "iCloud Download" to on (a cloud icon appears in the column titles)
- click on the cloud column icon to sort your songs by iCloud Download status
- scroll all the way up or down to see the songs that have a dotted cloud icon
- select one and play
- in the play progress bar (top middle of the iTunes window) click to advance playback to the middle or near the end
--> if the song is broken iTunes will just jump to the next one
- try with the next songs
- try to find a song that doesn´t have the dotted cloud and is also broken
The songs are cut off in the file (I checked with the Windows media player).
What is that "Waiting" status?
How can I fix that?