CB returning old data

Basically, we see old information from CB that after investigation we realized that data is OK, code is OK but the COVER INDEX for the involved query was returning wrong data. After drop and create index it worked fine.
couchbase.client.version: 3.4.0
CB Server version: 7.1.1 CE

Indexes are not updated synchronously. Usually the delay is very brief - a second or less. To ensure the indexes are updated to a particular point, use QueryScanConsistency=REQUEST_PLUS. See the documentation for other options.

The problem is NOT seconds or minutes. The data it returns is WRONG. We DO use the REQUEST PLUS scan consistency. To confirm that we run the same query adding some extra field check to break the COVER index and pick another normal GSI index and it worked as expected. So, we suspect that in the current version of our setup there is a bug in the COVER index. This is the 3rd time it happens in PROD that 1 doc is returned when there should not be and our workaround is to re-build the cover index to fix it.

It could be that the indexer stops working.
Please open an issue at issues.couchbase.com.

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Please let us know what addition details we can provide to get the issue resolved.

Provide the server logs.
Better yet, look in the server logs to see if there are issues with the indexer.