Invalid authentication message 'Unknown command' when persistent connections are used

2021-06-01 13:41:22   info   : (4608237) (Read-Write-Service) > Autocommit: [enabled], trx is [not open], cmd: (0x03) COM_QUERY, plen: 550, type: QUERY_TYPE_READ, stmt: SET STATE

MENT max_statement_time = 60 FOR 

       SELECT 

         posts.post_id 

       FROM phpbb.search_wordlist 

       LEFT JOIN phpbb.search_wordmatch ON 

         search_wordmatch.word_id=search_wordlist.word_id 

         AND search_wordmatch.title_match = 1

       LEFT JOIN phpbb.posts FORCE index (f_p_t_i) ON 

         posts.post_id=search_wordmatch.post_id 

         AND posts.forum_id = 36 

       WHERE 

         search_wordlist.word_text = '324021' 

       AND posts.post_time > UNIX_TIMESTAMP() - 86400 * 30 

       LIMIT 1

2021-06-01 13:41:22   info   : (4608237) (flea) Sent COM_CHANGE_USER

2021-06-01 13:41:22   info   : (4608237) [readwritesplit] (Read-Write-Service) Connected to 'flea'

2021-06-01 13:41:22   info   : (4608237) [readwritesplit] (Read-Write-Service) Route query to slave: flea <

2021-06-01 13:41:22   info   : (4608237) (flea) COM_CHANGE_USER in progress, appending query to queue

2021-06-01 13:41:23   error  : (4608237) Invalid authentication message from backend 'flea'. Error code: 1047, Msg : #08S01: Unknown command

2021-06-01 13:41:23   info   : (4608237) [readwritesplit] (Read-Write-Service) Slave 'flea' failed: #HY000: Lost connection to backend server: connection closed by peer (flea: Generated event)

2021-06-01 13:41:23   info   : (4608237) [readwritesplit] (Read-Write-Service) Re-routing failed read after server 'flea' failed