FTS: rollback not happening - FTS not catching up with KV

Build: 7.0.0-5017
Test Suite: moving-topology-scorch_5.5_P1
Rollback Tests:

./testrunner -i /tmp/testexec.21146.ini -p get-cbcollect-info=False,disable_HTP=True,get-logs=False,stop-on-failure=False,GROUP=P1,index_type=scorch,fts_quota=990 -t fts.moving_topology_fts.MovingTopFTS.partial_rollback,cluster=D,D,F,items=50000,update=True,upd=30,upd_del_fields=['dept'],GROUP=P1,get-cbcollect-info=False,disable_HTP=True,get-logs=False,stop-on-failure=False,index_type=scorch,fts_quota=990

./testrunner -i /tmp/testexec.21146.ini -p get-cbcollect-info=False,disable_HTP=True,get-logs=False,stop-on-failure=False,GROUP=P1,index_type=scorch,fts_quota=990 -t fts.moving_topology_fts.MovingTopFTS.partial_rollback,cluster=D,D,F,items=50000,delete=True,del=10,GROUP=P1,get-cbcollect-info=False,disable_HTP=True,get-logs=False,stop-on-failure=False,index_type=scorch,fts_quota=990

Test steps:

• Cluster setup : n1:kv, n2:kv, n3:search
• Load 50000 with field and value : mutated:0
• Create default index
• Stop persistence on both kv nodes
• Update 15000 docs with mutated:1
• Get the query count before rollback: {"query": "mutated:>0"}

  which is 15000

• Kill memcached on n1
• start persistence on n2
• Failover n2
• Kv rolled back and updated 15000 docs reverted back to before update. So they reverted back to mutated:0
• We expect FTS index also should rollback and update the index along with kv. But its not.
• Query {"query": "mutated:>0"}

  returns 15000, but in KV there are 0 docs

curl -XGET  http://172.23.96.141:8094/api/nsstats -u Administrator:password | jq | grep rollback

  % Total    % Received % Xferd  Average Speed   Time    Time     Time  Current

                                 Dload  Upload   Total   Spent    Left  Speed

100  3594    0  3594    0     0  20078      0 --:--:-- --:--:-- --:--:-- 20191

  "default:default_index:timer_rollback_count": 0,

  "tot_rollback_full": 0,

  "tot_rollback_partial": 0,

Attached screenshot where mutated:1 returns 15000 results, but actually looking into the doc, mutated is 0

Logs:

https://cb-jira.s3.us-east-2.amazonaws.com/logs/rollback/collectinfo-2021-04-29T003740-ns_1%40172.23.96.141.zip [FTS]
https://cb-jira.s3.us-east-2.amazonaws.com/logs/rollback/collectinfo-2021-04-29T003740-ns_1%40172.23.97.211.zip [KV]
https://cb-jira.s3.us-east-2.amazonaws.com/logs/rollback/collectinfo-2021-04-29T003740-ns_1%40172.23.97.212.zip [KV]