The odd old aged...oddity mystery bug..."Missing files"....Yep seen that in a older x3 rendition I believe.
And others saying odd things happening yet are very hard to reproduce...
So many things of odd natures that should not happen...Happen...I Guess some one named Murphy put his laws of code into the machines...
Sorry bud, if it ain't in the folder, and windows search for track name and number does not resolve, try to see what the file location is set to when you open the last session, in the preferences....if it has changed...You might find it in some way liken that?...or if auto save has a different folder choice and check that?
Also of remembered notes of past use..... I bumped into a tile with numbers on it up on the right side of the DAW...selecting the numbers changes the view of the track view, hides things, and or...another oddity may occur and some windows close or hide...Yet cannot be returned to view as nothing is hidden....So, clicking around to see what does what...That tile with lots of numbers on it, seems to do something in changing views, nd hiding tracks....go through those numbers...and see if your track appears again....
Just a thought...
Some times we hit the wrong hot keys by mistake...trying to stop the play or record....oops.
Best wishes!
Cheers.