The Billable Services total for a project seen in Create Batch Invoice screen does not match the total of the Amounts from the time entries that are being billed.
This can happen if there is a Write-Up/Down (WUD) on the time entries. As of now, the Amount field in the Time Entries and Time Entry Details screens does not include WUD, it only includes taxes. So if there is a WUD on the entries, it is not reflected in their amounts. If you want to see the actual amount that is billed for a time entry, you can do that using the Charge Amount field in the Time & Expense Reviewer screen (More > Show/Hide Columns > Charge Amount). Check the Core Help for details.
Note: If you think the time entries should not have a WUD, you can set it back to zero. The time entry amounts then match the amounts being billed. Check out this article on how to reset the WUD: Resetting write up/down on invoices. You can also batch update the WUD to zero from the Time Entries screen. Check out the Core Help for more on that.