The above is not an indication of fractional reserve. Likely explanation: Customer funds are divided between hot/cold wallets where only a fraction is immediate

The above is not an indication of fractional reserve. Likely explanation: Customer funds are divided between hot/cold wallets where only a fraction is immediately available for withdrawal, and a separate process (at most exchanges involving manual approval, not sure about Coinbase) is required to move top it up with funds from cold storage. It's a security thing to limit impact of hacks etc. If you need assets to be immediately available to make on-chain transactions, you should not keep them under custody of centralized exchanges - they can and will delay withdrawals for a variety of reasons and most of them (including CB) do make this clear in ToS. Now with Travel Rule regulation coming in (CB already started enforcing this in some countries but it will become mostly global over time), you need to specify name and physical address of recipient when withdrawing and this can be subject to manual checks as well, so withdrawals being delayed will become the norm IMO.