Only one parent can claim a dependent if filing separately. The IRS stated that the parent who claims the dependent gets the check. They thought that should simplify matters but I've heard of custody situations where parents alternate dependency claims. That means that the parent who claimed in 2019 got the check, but the claiming parent in 2020 will actually have the dependent on their return.
How will that work? The parent claiming in 2019 will have been overpaid (since the dependent isn’t on their return), will they have to give $500 back?
The parent claiming the dependent didn’t get a check, I can’t see how they’d be denied the credit.