FTS query returns "search request rejected" 6.0.0-1484

Search query from SDK and UI returns following message instead of search result.

search request rejected","request":{"ctl":{"consistency":null,"timeout":9499},"explain":true,"facets":null,"fields":["*"],"from":0,"highlight":{"fields":null,"style":null},"includeLocations":false,"pindexNames":["ftsIndex_6dc7bf54169cbbda_f4e0a48a","ftsIndex_6dc7bf54169cbbda_18572d87"],"query":{"query":"SampleValue1"},"size":10,"sort":["-_score"]},"status":"fail"}

Steps to reproduce:
1. install 6.0.0-1484 with 4 node cluster (data/index/query/search)
2. create 'default' bucket and add 1501 items. one of the documents contains "SampleValue1"
3. create fts index against 'default' bucket.
4. go to fts UI and select the fts index created in #3
5. In search input, put "SampleValue1"

Expected: 1 document should be listed
Actual : search request rejected

6.0.0-1432 worked fine.