I'm using BV6300 pro and google familylink for both of my kids and it looks like these phones do not ring when the daily limit is used and phones are locked.
They do vibrate when the settings are configured to do so and you try to call them, but no ringing. Once I unlock the phones, then all works normally.
The same is not happening on other phones with familylink.
It can't be some weird setting my kids have accidentally played with, as both BV6300 phones act the same way.

Any suggestions?

This is really wierd. Maybe you should not use familylink...