To my knowledge, no citizen has ever been prevented from reentry due to a blank or absent device. In fact they cannot block a citizen’s legal reentry for any reason, they can only detain you while they investigate.

Beyond this, “I dropped my phone in the ocean” is always a perfectly valid reason.

If you’re a foreigner and they already suspect you of something, they can deny you entry for any reason. It may be better to be denied than arrested!

No citizen afaik. Foreigners yes, afaik. Bad, but materially different... but slippery slope arguments are rather predictive with the current government controllers.