Server random crash on ALTER TABLE

MariaDB server is randomly crashing when ALTERing a table (adding a column), cannot always reproduce. Table is not useble after the crash and data is lost. Command used before the last crash:
ALTER TABLE `invoices`
ADD `proforma_invoice_amount_used` FLOAT NOT NULL,
COMMENT='';

Attaching these files:
syslog.log - crash log from syslog
global_variables.txt - output from 'show global variables'
table.txt - altered table original definition
my.cnf - server config file
invoices.ibd - idb file from table which was altered
#sql-6493_f2aac.frm - temporary frm file from table which was altered (the original one was missing)