mysql 5.6 InnoDB: Error (Duplicate key) writing word node to FTS auxiliary index table. (no replies)

Hello.
Please tell me how to fix this error?
Why is this error created?

My system.
FreeBSD 12.0-RELEASE-p9 amd64

My base server.
mysql Ver 14.14 Distrib 5.6.45, for FreeBSD12.0 (amd64) using EditLine wrapper

I see a lot of errors in the mysql log.
2019-10-15 20:41:53 e1498d900 InnoDB: Error (Duplicate key) writing word node to FTS auxiliary index table.
2019-10-15 20:57:33 e1498d900 InnoDB: Error (Duplicate key) writing word node to FTS auxiliary index table.
2019-10-15 20:57:33 e1498d900 InnoDB: Error (Duplicate key) writing word node to FTS auxiliary index table.
2019-10-15 22:03:08 e1498d900 InnoDB: Error (Duplicate key) writing word node to FTS auxiliary index table.
2019-10-15 22:03:08 e1498d900 InnoDB: Error (Duplicate key) writing word node to FTS auxiliary index table.
2019-10-15 22:41:54 e1498d900 InnoDB: Error (Duplicate key) writing word node to FTS auxiliary index table.
2019-10-15 22:41:54 e1498d900 InnoDB: Error (Duplicate key) writing word node to FTS auxiliary index table.