Mariadb hangs, stops responding to new connections

During my daily mysqldump (called by the Debian automysqlbackup script) a few times per week mysql hangs. The TCP listener and socket stay up but no longer accept new queries. The only resolution is to kill -9 the mysqld process.

I was able to do a gdb stack trace in this state, see attachments.

The Debian bug report is https://bugs.debian.org/cgi-bin/bugreport.cgi?bug=943962

The error.log says:

corrupted size vs. prev_size
191108 7:22:01 [ERROR] mysqld got signal 6 ;
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: 10.3.17-MariaDB-0+deb10u1-log
key_buffer_size=134217728
read_buffer_size=131072
max_used_connections=6
max_threads=65546
thread_count=7
It is possible that mysqld could use up to
key_buffer_size + (read_buffer_size + sort_buffer_size)*max_threads = 142762793 K bytes of memory
Hope that's ok; if not, decrease some variables in the equation.

Thread pointer: 0x7f33e4178cc8
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...
stack_bottom = 0x7f341981ace8 thread_stack 0x49000

My query.log has this right before the crash:

13019 Init DB drupal6
13019 Query SHOW CREATE DATABASE IF NOT EXISTS `drupal6`
13019 Query SHOW TABLES LIKE '%'
13019 Query LOCK TABLES `access` READ /!32311 LOCAL */,`accesslog` READ /!32311 LOCAL /,`actions` READ /!32311 LOCAL /,`actions_aid` READ /!32311 LOCAL /,`advanced_help_index` READ /!32311 LOCAL /,`authmap` READ /!32311 LOCAL */,`ba
tch` READ /!32311 LOCAL */,`blocks` READ /!32311 LOCAL /,`blocks_roles` READ /!32311 LOCAL /,`boxes` READ /!32311 LOCAL /,`cache` READ /!32311 LOCAL /,`cache_block` READ /!32311 LOCAL /,`cache_content` READ /!32311 LOCAL /,`cache_filter` READ /!323
11 LOCAL /,`cache_form` READ /!32311 LOCAL /,`cache_menu` READ /!32311 LOCAL /,`cache_page` READ /!32311 LOCAL /,`cache_update` READ /!32311 LOCAL /,`cache_views` READ /!32311 LOCAL /,`cache_views_data` READ /!32311 LOCAL /,`comments` READ /!32311
LOCAL /,`content_group` READ /!32311 LOCAL /,`content_group_fields` READ /!32311 LOCAL /,`content_node_field` READ /!32311 LOCAL /,`content_node_field_instance` READ /!32311 LOCAL /,`content_type_event` READ /!32311 LOCAL */,`date_format_locale` READ /
!32311 LOCAL */,`date_format_types` READ /!32311 LOCAL /,`date_formats` READ /!32311 LOCAL /,`files` READ /!32311 LOCAL /,`filter_formats` READ /!32311 LOCAL /,`filters` READ /!32311 LOCAL /,`flood` READ /!32311 LOCAL /,`history` READ /!32311 LOCAL
/,`image` READ /!32311 LOCAL /,`image_attach` READ /!32311 LOCAL /,`img_assist_map` READ /!32311 LOCAL /,`languages` READ /!32311 LOCAL /,`locales_source` READ /!32311 LOCAL /,`locales_target` READ /!32311 LOCAL /,`menu_custom` READ /!32311 LOCAL
/,`menu_links` READ /!32311 LOCAL /,`menu_router` READ /!32311 LOCAL /,`messaging_message_parts` READ /!32311 LOCAL /,`messaging_store` READ /!32311 LOCAL /,`modr8_log` READ /!32311 LOCAL /,`node` READ /!32311 LOCAL /,`node_access` READ /!32311 LOC
AL /,`node_access_role` READ /!32311 LOCAL /,`node_access_user` READ /!32311 LOCAL /,`node_comment_statistics` READ /!32311 LOCAL /,`node_counter` READ /!32311 LOCAL /,`node_revisions` READ /!32311 LOCAL /,`node_type` READ /!32311 LOCAL */,`notificat
ions` READ /!32311 LOCAL */,`notifications_event` READ /!32311 LOCAL /,`notifications_fields` READ /!32311 LOCAL /,`notifications_queue` READ /!32311 LOCAL /,`notifications_sent` READ /!32311 LOCAL /,`permission` READ /!32311 LOCAL /,`poll` READ /!32
311 LOCAL /,`poll_choices` READ /!32311 LOCAL /,`poll_votes` READ /!32311 LOCAL /,`revision_moderation` READ /!32311 LOCAL /,`role` READ /!32311 LOCAL /,`search_dataset` READ /!32311 LOCAL /,`search_index` READ /!32311 LOCAL */,`search_node_links` RE
AD /!32311 LOCAL */,`search_total` READ /!32311 LOCAL /,`semaphore` READ /!32311 LOCAL /,`sessions` READ /!32311 LOCAL /,`system` READ /!32311 LOCAL /,`term_data` READ /!32311 LOCAL /,`term_hierarchy` READ /!32311 LOCAL /,`term_node` READ /!32311 L
OCAL /,`term_relation` READ /!32311 LOCAL /,`term_synonym` READ /!32311 LOCAL /,`trigger_assignments` READ /!32311 LOCAL /,`upload` READ /!32311 LOCAL /,`url_alias` READ /!32311 LOCAL /,`user_import` READ /!32311 LOCAL /,`user_import_errors` READ /
!32311 LOCAL /,`users` READ /!32311 LOCAL /,`users_roles` READ /!32311 LOCAL /,`variable` READ /!32311 LOCAL /,`views_display` READ /!32311 LOCAL /,`views_object_cache` READ /!32311 LOCAL /,`views_view` READ /!32311 LOCAL /,`vocabulary` READ /!3231
1 LOCAL /,`vocabulary_node_types` READ /!32311 LOCAL /,`watchdog` READ /!32311 LOCAL /,`workflow_access` READ /!32311 LOCAL /,`workflow_node` READ /!32311 LOCAL /,`workflow_node_history` READ /!32311 LOCAL /,`workflow_scheduled_transition` READ /!323
11 LOCAL /,`workflow_states` READ /!32311 LOCAL /,`workflow_transitions` READ /!32311 LOCAL /,`workflow_type_map` READ /!32311 LOCAL /,`workflows` READ /!32311 LOCAL /,`wysiwyg` READ /!32311 LOCAL /,`xmlsitemap` READ /!32311 LOCAL */,`xmlsitemap_node
` READ /!32311 LOCAL */,`xmlsitemap_taxonomy` READ /!32311 LOCAL */
191108 7:22:01 13019 Query SELECT engine FROM INFORMATION_SCHEMA.TABLES WHERE table_schema = DATABASE() AND table_name = 'access'
[snip]
13019 Init DB drupal6
13019 Query select @@collation_database
13019 Query SELECT TRIGGER_NAME FROM INFORMATION_SCHEMA.TRIGGERS WHERE EVENT_OBJECT_SCHEMA = DATABASE() AND EVENT_OBJECT_TABLE = 'url_alias'
13019 Query SET SESSION character_set_results = 'utf8mb4'
13019 Query SELECT engine FROM INFORMATION_SCHEMA.TABLES WHERE table_schema = DATABASE() AND table_name = 'user_import'
13019 Query SET SQL_QUOTE_SHOW_CREATE=1
13019 Query SET SESSION character_set_results = 'binary'
13019 Query show create table `user_import`
13019 Query SET SESSION character_set_results = 'utf8mb4'
13019 Query show fields from `user_import`
13019 Query SELECT /*!40001 SQL_NO_CACHE */ `import_id`, `name`, `filename`, `oldfilename`, `filepath`, `started`, `pointer`, `processed`, `valid`, `first_line_skip`, `contact`, `username_space`, `send_email`, `field_match`, `roles`, `options
`, `setting` FROM `user_import`