BQ40Z50-R2: Battery shows low FCC

Part Number: BQ40Z50-R2

Hello experts,

I got question about FCC from customer. 

Their battery sometimes shows a low FCC.
When this low FCC is shown, it reaches 0% faster than usual, so the battery capacity that can be used is reduced.

As a result of checking the state of the Battery 1 with a low FCC, the Filtered FCC was low. But True FCC was not low.
So they think the cause of low FCC is caused by Filtered FCC, so they would like to ask about this cause. Could you please tell me about the following:

・ Could you tell me why the Filtered FCC is low?
・ How can I restore the low Filtered FCC?
・ Although Battery 2 has reduced True FCC, but Qmax is high. Could you tell me why this happens?

Thanks and best regards,

Ryo Akashi