Inconsistency between Syncgateway index and its replica

Couchbase v6.6.2
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We tried to move the sg indexes to other nodes via ALTER INDEX. The indexes have been recalculated and now are consistent with each other.
sg_channels_x1 went from 18mln to 10mln
also sg_tombstones_x1 went from 18mln to 600k (see Compacting bucket does not purge tombstoned document - #4 by losapevo)
I saw that sg indexes have this option "retain_deleted_xattr":true. Because of that option, could it be that when tombstones are purged, indexes are not updated and increase forever?