Don’t worry, it’s not gone forever. It’ll be picked up at the next matching event and the issue will be resolved when you get your first repayments.
When you initially invest with Zopa, your funds can be first matched to loans in progress that other lenders (looking to make a withdrawal, for example) are selling. These are rarely nice round numbers and so your pennies can be split down to 8 decimal places. We can only give you money for full penny amounts: so when we come to calculate your Zopa Total (deposits + withdrawals), we prefer to be conservative, and round these pennies down: hence the temporarily missing copper, which corrects itself with your first repayments.