It's possible to roll back to a previous version of Android, but that essentially will result in a factory reset device. I suggest following the same data backup and then do a factory reset of the newer, more secure, version of Android and see if it fixes your problem.
Here's how to do the re-flash:
https://forums.androidcentral.com/am...interface.html
Before doing that, you could also try wiping the cache partition.
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