Android 10: unable to change AppStandbyBucket status for any apps

I have two OnePlus 7Pro devices, both running OOS 10.3.8 and both rooted. On one of these devices, I can go to ***Settings=>System=>Developer options=>Standby apps***, and in the resulting list of installed apps, I can successfully change the status of any app from "ACTIVE" to other values ("WORKING_SET", "FREQUENT", "RARE"). On the other device, when I go to ***Settings=>System=>Developer options=>Standby apps***, I also see the list of installed apps, but all are showing as "ACTIVE", and when I try to change that status for any app, the status does not change, and it remains "ACTIVE". This unchangeability persists after reboots. I have been trying to deal with doze-related issues on the second device, and I'm guessing that one of the many things I was experimenting with might have caused AppStandbyBucket values to become unmodifiable. What could I have done on this second device to prevent the Standby-app status from being changeable? ... and what can I do on that device to enable those status values to be changed? Thank you in advance for any thoughts and suggestions. **PS**: I'm wondering if there might be some config file somewhere on the device which should be writable, but whose permissions might have gotten changed to read-only. Is that possible? If so, what could be the file (or files) in question?