Not sure what fixed it but I uninstalled, reinstalled 1.7 and then updated and it fixed itself. My assumption would be there's a package missing in the new update.
I just tried to reproduce your problem, and Export to X3G displays just fine on a fresh Replicator 2 profile. My guess is that somehow under SETTINGS > Printer > Features, the Sailfish Communication box came unchecked, as that is the setting that triggers whether or not the Export as X3G option appears in the QUEUE menu.
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