This sounds troubling and it's a little disappointing to see comments suggesting "factory resets before travel" or "dual booting". These are not things anyone really wants to have to do.
Also, this issue raises some more questions:
1) It sounds like they might use a device to scan your hardware automatically, potentially opening the door to copying files for permanent record
2) It is a small step from here to install tracking software on your device (as China is doing in some places)
Other than fixing the actual problem (the overreaching legislation/government), the only other solution seems to be using a burner phone when traveling. I would absolutely not trust any device handed to an official, even if it was factory reset and I had a backup.
How do we know that they aren't installing software? It may just be a matter of time before someone reports an incident in which another one of these nations do install something.
Also, this issue raises some more questions:
1) It sounds like they might use a device to scan your hardware automatically, potentially opening the door to copying files for permanent record
2) It is a small step from here to install tracking software on your device (as China is doing in some places)