I have the same exact issue. At a certain time of day I have a time limit that goes out, and if I want to request more screen time from my guardian I can't. I know it's not an Apple ID issue because I can do all of it from my MacBook (not running a beta version of MacOS), and my only option on my iPhone is to enter the screen time passcode. Upon doing that when more time is approved by my guardian, I cannot use the time that I have been given. I'm pretty sure it's the beta that's doing this, and it's gotten so annoying that I'm actually considering uninstalling the beta. The only problem with that is that I have important files on my iPhone, and I literally have a partitioned volume on an external HDD I made just for iPhone backups. I can't back up the files because of the beta, though, and I can't backup my iPhone to iCloud due to insufficient space, If I get the 50GB option I should be good, but I'm not sure if I will quite yet. So I'm kind of stuck as to what to do here. Public beta apparently got released yesterday, I'll try installing that and see if the issue persists.