MariaDB performance issues

Server version: 10.2.27-MariaDB MariaDB Server

hello - i am really not much of a DBA, more of a programmer who also has responsibility for the db.

very recently MariaDB seems to occasionally "crash" and leaves our db's in a corrupted state. this started happening perhaps after an upgrade(?). i did yum-remove all MariaDB stuff, including the db's themselves and used yum-install to reinstall everything.

i ran `MySQLTuner-perl` and i see the following:

[!!] /var/log/mariadb.err.log contains 1 warning(s).
[!!] Query cache may be disabled by default due to mutex contention.
[!!] Query cache efficiency: 0.0% (0 cached / 1 selects)
[!!] Key buffer used: 18.2% (24M used / 134M cache)
[!!] InnoDB buffer pool / data size: 512.0M/576.5M
[!!] InnoDB Read buffer efficiency: 23.03% (2562 hits/ 11127 total)
[!!] InnoDB Write Log efficiency: 0% (2 hits/ 0 total)

and here is my.cnf:

[mysqld]
sql_mode=NO_ENGINE_SUBSTITUTION
innodb_log_file_size = 64M              # 2019-10-14
max_allowed_packet = 64M                #   2019-10-14
skip-name-resolve                       ## 2019-10-16
innodb_buffer_pool_size = 512M
table_definition_cache = 1000000        # 2019-10-14 - changed from 400 (default)
skip-networking=0        #skip-networking=1         ## added 2019-05-09
plugin_load_add = server_audit
log_error=/var/log/mariadb.err.log      ## added 2019-06-13

any suggestions on how to proceed?