Replication.ChangeListener didn't call immidiate at Background handler thread

Into a Handler Thread , i have created new Database , then created replication then start pull and added a pull ChangeLister . it called very late max 1 minute . Where is the problem ? I am working Couchbaselite android 1.4. I need urgent help .

A replication change listener performs callbacks when the state of a replication changes. A replication may take some time to change. This is especially true when first syncing.

How many documents are you expecting to replicate? Have you looked at the sync gateway logs to see what’s happening in the other end?

more than 2000 , but problem is in Android 8 SDK 26 or up . when light is off the device , it can’t start sync . How can i solve this issue? I can active device from background . Some times sync works and sometimes not . Sometimes it takes more than 5 minutes . I want to update CBL into 2.0 . Do i need any extra version for couchbase server for this ?

Also I want to delete _rev history . Can you pls tesll what is the way to remove _rev history ?