There is an Issue with river build and has been already reported. The team is checking on this. Have requested them to withdraw the build from the servers. Will update if there are any inputs.
Requesting users of Moto G7 river if you have reverted to v1.21 pl can you do the following
- enable root in Developer settings
run this command from a PC console
adb root
adb pull /cache/recovery/last_log
or
logs just after the reboot for the update with
adb logcat
Attach the log files to the issue created here