Galera cluster randomly hangs

Question

Hello I have a Galera cluster for MySQL 5.6.36 that apparently works fine. I have a microservice with a REST API running in Docker that is connected via JPA + Hibernate to this database. Randomly, the service takes about 15 min to produce the response (all the time is taken by the database operation). I've tried to check most common MySQL and Galera status information but I don't see anything bad in the values, cluster seems to work well and also replication. The query is really simple (a select on a table) and what is really strange is that I don't see anything about that query if I run show processlist in MySQL. Can you suggest me a way to debug this problem considering that it's also very difficult for me to replicate it (apparently it happens randomly without any correlation with the load).