FaceID failing in iOS 17.5 B2 on iPhone 12 mini

FaceID fails with "Problem with TrueDepth camera" in iOS 17.5 B2 on an iPhone 12 mini.

I've erased the phone and restored from iCloud backup, and though it began to work again properly, FaceID soon failed again - maybe after an hour or two. I don't believe this is a TrueDepth camera hardware problem. I've erased and restored a second time and I expect it to fail again.

I'd like to downgrade to 17.4.1 but the erase/restore procedure installs the beta, even when I deselect the Developer Beta option.

Anyone else seeing this?

TIA