Noticed this myself as well - I've been actively doing every World Quest across Argus every day, and only have two Argrussian World Quests up now (one normal + one pet battle). I've sent an ask about this over to the development team, so I'll let you know when I hear something official.
I've also asked for clarification on the intent/rule behind "should there always be enough world quests up to immediately complete a new Emissary".
Edit: In the mean time, be patient, as I'm sure more will spawn through the day.
Thanks for your patience everyone - a hotfix is live as of about 15 minutes ago to require the Argussian Reach Emissary Quest to only require three World Quests to complete. There's currently an issue where the text will show as four needed, but it should complete at three.
This is being done temporarily, until next week, at which more Argussian Reach World Quests should be available and the Emissary Quest requirement for this faction will be reverted back to require four.
I'm seeing two on Mac'Aree and one in Krokuun currently, as of this writing.
Another issue is that some rare boss World Quests may count for both Army of Light and Argussian Reach, but may only show one or the other at the moment, as the UI doesn't seem to want to support showing both. This is something we're looking into, but in the mean time I suggest trying some of the Army of Light rares and seeing if they count.
It's not intended that you would need to Pet Battle or turn in crafting materials to complete this Emissary.