Galera node hang - wsrep applier thread command "Busy" with state "innobase_commit_low()"

Our environment is 3 nodes Galera cluster - 2 DB nodes + 1 arbitrator
one DB node hung (state "Filling schema table") when running show status command. Galera cluster encountered flow control. We can still run "show processlist" and "select * from information_schema.innodb_trx" in this DB node.

DB error log is empty

Checked one galera slave thread was running command "Busy" with state "innobase_commit_low()" in this DB node.

|      96 | system user    |                                                      |      | Busy    |    6673 | innobase_commit_low()                   | NULL                                      |    0.000 |

tried to kill the slave thread but command hung

We finally restart the DB node to resume

any idea what caused this issue ?
attached processlist and "select * from information_schema.innodb_trx"