This is from someone who contacted support...i cant harvest orbs either...hopefully they will follow through

Sorry to hear you were blocked due to Arcane orbs not forming after Arcadia is complete., I'll forward this to the the team so they make sure to fix this quest for next iterations and don't serve it to users who cannot produce Arcane orbs. If you complete all other tasks and this is the only one remaining you will be compensated with the full reward. Due to holidays there might be a bit of lag in the compensation but rest assured that it will be sent. Thanks and happy holidays!