Hi Vijendra.
Actually it seems that it succeeded in overcoming the “Exception in EncryptionKeyDB::init: {e}” problem when you restarted. It moved on and shows “Initializing KeyDB with wiredtiger_open config: {cfg}” instead. So that is progress.
The error you’re at now is: having loaded a key it finds existing WiredTiger data files and tries to decrypt them.
Trying to use keys with existing data files that were made without encryption won’t work. You get the error you see above (“unable to read root page from file” + “This may be due to the database files being encrypted”).
When you first enable the keys you should restart with an empty db directory path. Which means restart in an existing replicaset to sync existing database collections from the other members that haven’t begun to use data-at-rest encryption yet. Or making a new, empty replica set.