Couchbase Server Enterprise 7.0 Backup UI service's Merge issue

Recently I setup Couchbase Server Enterprise 7.0 with 3 nodes ( Rhel8). My cluster backup is setup with NFS server is the same subnet. Was using the Backup UI and default hourly Plan to do backup and merge of Travel-Sample bucket. The Full backup and incremental backup perform very well without issue but the 6 hourly merge is taking very long. Many time failed with task is orphaned or taking too long and failed with another task is running. Not sure what is happening here. Take for example the full backup of travel-sample tool only less than 2 minutes, but the merge of two or more travel-sample will take more than few hours or even more. Looking at the task it did complete the merge as in 1/2 then 2/2 , there is end time for 2/2 merge which is quite fast also less than 10 mins. But the overall end datetime is 00T00… no datetime. Could somebody advise me what I need to do to get it right?