In some cases databases gets corrupted(shit happens). After a hardware fail or not correct usage like a “kill -9” of mysqld process without gracefully flushing of opened tables.
After the start of mysqld.service, you can get a log-entry in your mysqld-log file, which informs you about the corruption of database, like this one “corruption in the InnoDB tablespace“.
In some cases mysqld.service will crash every n-minutes..
Independently of the symptoms the crashed database should be repaired immediately!