The IRS will use 2019 information if 2020 information is not available so if your return is still being processed, it’s not yet in the IRS system.
The IRS did send out catch-up payments for the previous stimulus to about 50,000 individuals whose portion of the EIP was diverted to pay their spouse's past-due child support so you may get your third stimulus on time.
Related Resources:
IRS: 50,000 spouses to get catch-up Economic Impact Payments