I was editing the OnePlus 3T build.prop file when I encountered the DM-verity warning. This is part of the verified boot process. More details can be read here.
There were several posts to use the following to turn off and turn on DM-verity as a reset. Unfortunately, that only gives an error, “FAILED remote:unknown command”
fastboot oem disable_dm_verity
fastboot oem enable_dm_verity
After some searching, some on recommended,
adb reboot “dm-verity enforcing”
That caused the device to restart.
I have found by accident, even with the dm_verity error, if I don’t do anything the phone eventually boot.