The customer reported that stop slave caused the master down/crash. During my repro, I was able to see that master got crashed once slave stopped manually.
The followings are the error log from master and slave when slave was stopped manually.
For testing purpose, sysbech was run against backend server via 2 maxscale servers.

• 200 threads with 90:10 (write/read workload) - port : 2582
• 200 threads with 1000 (read only workload) - port : 2482

• on master

  2023-01-31 8:55:59 4481 [ERROR] Semi-sync master failed on net_flush() before waiting for slave reply

  2023-01-31 8:55:59 4481 [Note] Stop semi-sync binlog_dump to slave (server_id: 2)

  2023-01-31 8:56:00 4481 [Warning] Aborted connection 4481 to db: 'unconnected' user: 'repl' host: '192.168.254.53' (Failed to run hook 'after_send_event')

  2023-01-31 8:56:09 4204 [Warning] Timeout waiting for reply of binlog (file: mariadb-bin.000001, pos: 214503559), semi-sync up to file mariadb-bin.000001, position 214503085.

  2023-01-31 8:56:09 4204 [Note] Semi-sync replication switched OFF.

  2023-01-31 8:56:09 4901 [Warning] Aborted connection 4901 to db: 'unconnected' user: 'unauthenticated' host: '192.168.254.53' (Got an error reading communication packets)

  2023-01-31 8:56:09 4901 [Warning] Aborted connection 4901 to db: 'unconnected' user: 'unauthenticated' host: '192.168.254.53' (This connection closed normally without authentication)

  2023-01-31 8:56:09 4346 [Warning] Aborted connection 4346 to db: 'unconnected' user: 'mxs' host: '192.168.254.54' (Got an error reading communication packets)

  2023-01-31 8:56:09 4903 [Warning] Aborted connection 4903 to db: 'unconnected' user: 'unauthenticated' host: '192.168.254.55' (Got an error reading communication packets)

  2023-01-31 8:56:09 4903 [Warning] Aborted connection 4903 to db: 'unconnected' user: 'unauthenticated' host: '192.168.254.55' (This connection closed normally without authentication)

  2023-01-31 8:56:09 4904 [Warning] Aborted connection 4904 to db: 'unconnected' user: 'unauthenticated' host: '192.168.254.54' (Got an error reading communication packets)

  2023-01-31 8:56:09 4904 [Warning] Aborted connection 4904 to db: 'unconnected' user: 'unauthenticated' host: '192.168.254.54' (This connection closed normally without authentication)

  2023-01-31 8:56:09 4347 [Warning] Aborted connection 4347 to db: 'unconnected' user: 'mxs' host: '192.168.254.55' (Got an error reading communication packets)

  230131 8:56:10 [ERROR] mysqld got signal 11 ;

  This could be because you hit a bug. It is also possible that this binary

  or one of the libraries it was linked against is corrupt, improperly built,

  or misconfigured. This error can also be caused by malfunctioning hardware.

  To report this bug, see https://mariadb.com/kb/en/reporting-bugs

  We will try our best to scrape up some info that will hopefully help

  diagnose the problem, but since we have already crashed,

  something is definitely wrong and this may fail.

  Server version: 10.5.16-11-MariaDB-enterprise-log

  key_buffer_size=33554432

  read_buffer_size=131072

  max_used_connections=408

  max_threads=65537

  thread_count=301

  It is possible that mysqld could use up to

  key_buffer_size + (read_buffer_size + sort_buffer_size)*max_threads = 143409586 K bytes of memory

  Hope that's ok; if not, decrease some variables in the equation.

  Thread pointer: 0x7f4388437248

  Attempting backtrace. You can use the following information to find out

  where mysqld died. If you see no messages after this, something went

  terribly wrong...

  2023-01-31 8:56:15 0 [Note] mariadbd: Aria engine: starting recovery

  recovered pages: 0% 25% 59% 92% 100% (0.0 seconds); tables to flush: 1 0

  (0.0 seconds);

  2023-01-31 8:56:15 0 [Note] mariadbd: Aria engine: recovery done

• on slave

  2023-01-31 8:55:59 6387 [Note] Error reading relay log event: slave SQL thread was killed

  2023-01-31 8:55:59 6387 [Note] Slave SQL thread exiting, replication stopped in log 'mariadb-bin.000001' at position 214503085; GTID position '0-1-370185'

  2023-01-31 8:55:59 6387 [Note] master was 192.168.254.52:3306

  2023-01-31 8:55:59 6386 [Note] Slave I/O thread exiting, read up to log 'mariadb-bin.000001', position 214503085; GTID position 0-1-370185

  2023-01-31 8:55:59 6386 [Note] master was 192.168.254.52:3306

  2023-01-31 8:56:01 6386 [Note] cannot connect to master to kill slave io_thread's connection

  2023-01-31 9:01:12 6340 [Warning] Aborted connection 6340 to db: 'unconnected' user: 'root' host: 'localhost' (Got timeout reading communication packets)

This can be reproducible in 10.5.x and 10.6.x latest versions.