Hi Buttercp,
We appreciate you reaching out to us. We understand that you set your daughter's iPhone to allow only specific contacts during Downtime, but the setting keeps automatically reverting to everyone allowed.
We’d like to gather additional details that may help us be in a better position to assist you.
Are you using Family Sharing to manage your daughter's device? The article below may provide some insights.
Use Screen Time on your iPhone, iPad, or iPod touch
Also, we recommend that you check for a software update on your daughter's iPhone.
While it isn't inherently assured that an update will resolve the issue, updating to the latest software version for your device can help isolate potential software issues.
Kindly secure a backup and update.
How to back up your iPhone, iPad, and iPod touch
Update your iPhone, iPad, or iPod touch
Please keep us posted.
Take care!