It's an upgrade install from OTA. Should I do an 'Erase All Content and Settings' and then restore from an iCloud backup?
I can't say for certain, but I don't think that will work. Erasing All Content and Settings will leave your iPhone on iOS 10 Beta 1, which cannot be restored to an iCloud Backup from any iOS release prior to that, i.e. iOS 9.
In the case that you
have made an iCloud Backup since having installed the iOS 10 Beta, then you should be able to restore from the backup fine, but: a) I doubt this would fix your issue & b) I would not trust the iCloud Backup process to be working perfectly with backups generated from Beta iOS releases.
Hopefully, you had made either an iCloud Backup which you haven't overwritten, or an iTunes backup of your iPhone, just prior to installing the iOS 10 Beta. Hopefully, too, you were running the latest version of iOS, 9.3.2, when the backup was made. In that case, I would restore your phone in iTunes, so that iOS 9.3.2 is downloaded and installed onto your phone. I would then restore from this backup, and reinstall the OTA profile and update to the iOS 10 Beta again.