Hello, the same problem happened to me right now, but it is not related to any versions or updates in Guix. In fact, I just did an aggressive "guix gc", which removed the referenced exo version from the store. The path is actually stored in my $HOME/.config/xfce4/panel/launcher-19/15993349933.desktop which is not changed upon updating xfce. As long as the corresponding exo-open is still available in the store, clicking the icon will work; "guix gc" (after deleting the profile generations where this exo version was referenced) will remove it from the store.
I do not see what we could do inside Guix to solve the problem. Personally I simple replaced /gnu/store/*hash*-exo-0.12.6/bin/exo-open --launch *Applicationname* %u by *Applicationname* %u It works at least for (equal? *Applicationname* icecat). Andreas
