Hi,
I just noticed that my coinbase.com Wallet (via API) properly imports Fiat (EUR) deposits, but when I hover over the EUR icon in the Koinly wallet overview a lower amount is displayed than the total balance.
I verified this on coinbase.com and it seems you are displaying the "Available to Trade" or "Available to send or spend" balance value.
The difference is due to "open orders" in that currency.