[Si Coe]

I've had packs do that - just run it for a bit (but don't completely discharge so say 5 mins running or so) and try again.
Not quite sure why it happens, but that fixed it for me.

Oh, and TBH I only balance charge every 10 or so charges these days. The charger I use at race meetings doesn't actually do balancing, so I need to use my older charger for that which is why its not done often. Even so they are rarely if ever out of balance - probably because in a typical race we use no more than a quarter of the available capacity.