Bitcore customer, estimated transaction size of... 2600?!

I host a Bitcoin ATM and a Bitcoin wallet via Bitcore.

A customer has been paying up to $5 in order to send any amount of money (for example, even to send $5).

He receives 1 transaction from Coinbase, and he’s been dealing with this for months. He has $5 left in his account, but yet with fees it will cost more than $5 to send.

I know the underlying premise with how to calculate fees via bytes, and why there are bytes. My question is… is there a known issue with older (1y) versions of Bitcore? Is there a workaround aside from generating a new wallet for him?