Comment 4 for bug 1695793

I ran into the same issue. While not a fix, I found that if I can work around this with a symlink.

Just create a symlink with the name of the WM_CLASS you want that points to terminator. Call the symlink instead of terminator and it will update the WM_CLASS. This worked for me with gnome under wayland well enough to match to a .desktop file with StartupWMClass set