I fly the Mini 2 and have the charging hub for all three batteries with no problems.
When I charge a single battery in the hub, I find it takes almost 2 hours as opposed to say 45 minutes in the quad, at the same battery discharged state.
This is my findings and FYI.
Fly safe all.
Perhaps the charging speed inside the drone has been deliberately slowed down to avoid overheating the internal electronics, while the hub is unfettered?