Server Crash after Galera WSREP event received

We hava three nodes with Galera cluster. one day moring two of them crash due to "InnoDB: Rec offset 99, cur1 offset 10327, cur2 offset 15073" signal 6 message, and the backtrace includes "/usr/sbin/mysqld(start_wsrep_THD+0x29e)[0x7f41deb3858e]".

We start to investigate releated logs and gather some information below.
1. Two DB nodes crashed on 4/23 around 8:30 am.
2. "table A"'s index is currption.
3. There are still a lot of update or select sql from "table A" have been executed before db crashed.
4. The "table A" alter add "column C" VARCHAR(10) NOT NULL DEFAULT 'Y' without assigned algorithm on 4/22 around 2:00 am.
(our alter_algorithm value is DEFAULT. according to the Mariadb online document,
"the most efficient available algorithm will usually be used". so it might be "instant")
5. We don't have the currption .ibd file. but we have the dump sql file.
6. The "column C"'s data in "table A" should be empty,
but the insert sql "column C"'s value is wired,such as "010045]9`?"、"10044]ˏs10"、010049\"?.. etc... in the dump sql file.

We would like to know what caused our db crash.
Is it a innodb engine or galera cluster's bug?

Thanks.