I've been running Rocksmith 2014 via Steam on my Linux machine for a few years. I have noticed that randomly, official DLC songs in my game disappear and I can no longer find them in my song list to play. 

One example I just noticed is Radiohead's Creep - I've had that song for years in my Rocksmith playlist but noticed now it's gone. I checked Customforge and it's only listed as an official DLC for R+.

Is Ubisoft/Steam removing songs from my game without notifying me? Or is this a glitch/bug?

2 hours ago, ngpilot said:

Is Ubisoft/Steam removing songs from my game without notifying me?

Nope. Still there. Just to make sure there wasn't a wormhole or rip in the space time continuum, I just checked and played Creep on mine.

2 hours ago, ngpilot said:

Or is this a glitch/bug?

Yep. I mean, possibly. Most likely culprit is you accidentally or inadvertently selected a Sort Filter, like favorites. Start there first.

Actually has happened frequently to other peeps where people have had tracks just "disappear". Above is the usual culprit though as I said.

For 2014 songs you can go to the library page, select the DLC page, make sure that the song(s) in question are not un-ticked (check marked). Select, re-selecting the missing songs has in the past worked for other people in the past. Another solution is to verify files. There are more drastic solutions if those do not work, but I do not suggest doing that/those yet, as more than likely it is just a sort / filter issue.

same happened to me this week, queen-bohemian rapsody and Europe-Final Countdown have been removed. Possibly more. i have verified files and everything but didn't fix it.

I think this happened before and was fixed by updating Steam. Not sure that's the case now, but that's what the issue was before.