'Block at Downtime' not working

I am using Family Sharing to manage my teenage daughter's phone. Despite have a screen time passcode set, she can still "Ignore limits" on apps during downtime. I toggled on the "Block at downtime" feature, and this actually took away all limits and she could communicate using text and use all apps as if downtime was not on at all.

The only feature I have found to work to block the apps is by setting all app limits to 1 minute, but this is a realistic feature to use when she is not grounded. How do I get the 'Block at downtime' feature to work?