A first, I got a banner for a weekly mileage goal completion. The catch is that I’ve only ridden 17 miles of the 124. A great Monday surprise.
There used to be a forum topic about this but it was deleted. Not sure why but it’s been reported by others.
Hello @Richard_Traugott, thank you for flagging this up. I’ve seen this reported by a few Zwifters. Weekly goals are now functioning under fitness tracking, so this seems to be a new issue, but I’ve shared it with the appropriate team at Zwift HQ.
Still a problem,it has happened to me the last two weeks saying my weekly goal has been met 
after a only a few miles done.
Using Apple TV 4K and updated to the current version, I continue to get Weekly Goal Met banner at 22 minutes into my rides. Latest month is was around 32 minutes.
UPDATE February 24
Please update to game version 1.108 when phased rollout is available to your device. Please let us know if this is still occurring for you (or not).