Gvmd --optimize=cleanup-result-nvts always fails; other optimize commands works fine


Under Linux Mint / Ubuntu; gvmd 21.04 always fails optimizing result nvts.

md   main:MESSAGE:2021-07-17 00h03.24 utc:26654:    Greenbone Vulnerability Manager version 21.4.0~git-49b36f924-gvmd-21.04 (GIT revision 49b36f924-gvmd-21.04) (DB revision 242)
md manage:   INFO:2021-07-17 00h03.24 utc:26654:    Optimizing: cleanup-result-nvts.
md manage:WARNING:2021-07-17 00h03.29 utc:26654: sql_exec_internal: PQexec failed: ERROR:  more than one row returned by a subquery used as an expression
md manage:WARNING:2021-07-17 00h03.29 utc:26654: sql_exec_internal: SQL: UPDATE results SET nvt = (SELECT oid FROM nvts WHERE name = nvt),     result_nvt = NULL WHERE nvt IN (SELECT name FROM nvts WHERE name != oid);
md manage:WARNING:2021-07-17 00h03.29 utc:26654: sqlv: sql_exec_internal failed

Other optimizations works fine. Gvmd works fine. II have a crontab running this command on a weekly basis, and it systematically fails with the same error.

Anyone has a clue as to why this is happening ?