Yes, the feature sadly is more than a bit temperamental. One some configurations it works flawlessly, on others it throws a tantrum. Maybe I’ll reinstall Mac OS X on my iMac in the near future and try to deduce, where the problem lies.
Currently, you’ll sadly have to arrange with the fact that you’ll have to type everything manually in the gateway, to upgrade your installation of Whonix. Though, if you read this here completely, you’ll see that it isn’t as much as it may seem, since most things are “Qubes-Whonix specific”. Furthermore, may I recommend simply “reimporting” the newer Whonix 11 Gateway template? Since there shouldn’t be much changed in the Gateway (aside from at best ten lines in torrc) this may be an option.
Have a nice day,