Just lending my voice here for what it’s worth. I’m also completely surprised by the missing expression maps for track archives. (I’ve also noticed that they are missing if I import tracks from another project so it does not seem like this limitation is just for track archives.). It does not seem possible to preserve the expression maps on import in Cubase 11 Pro, no matter the method of import!
The problem persists but is apparently only an issue if your instrument tracks are inside a folder (which let’s be honest, all of ours are…). If they are not inside folders, the expression maps are preserved. This is likely the reason that some folks are reporting that they cannot reproduce the issue…
See: 10.5 Expression Maps no longer retained - #15 by lokotus