Couchbase XDCR from 4.6.1v to 3.1.5v showing weird behavior


I am using couchbase 3.1.5v enterprise edition. I have upgraded couchbase 4.6.1v on different cluster and enabled replication from 3.1.5v to upgraded version which is happening as expected. The other way (4.6.1v to 3.1.5v) is showing weird behavior, like it reaches 60% and then suddenly drops to 15% or even sometimes 0%. This replication never achieved 100%. Can some one help me resolve this issue If any one had observed and worked on this behavior with 4.6 version.