finding cause for sometimes slow query

I am trying to find the cause for a query that is slow, but only sometimes. I have slow query logging active, and I see the query being logged, for example:

timescaledb-2 timescaledb 2023-08-04 13:43:12 UTC : [64ccfe56.7f72-3] device_monitoring@postgres,app=PostgreSQL JDBC Driver  LOG:  duration: 27178.742 ms  bind S_9:

Sometimes the query times out, my client timeout is set to 30s, so I get:

timescaledb-2 timescaledb 2023-08-04 13:33:23 UTC : [64ccf76c.745c-3] device_monitoring@postgres,app=PostgreSQL JDBC Driver  ERROR:  canceling statement due to statement timeout

Running [explain on the query](https://explain.dalibo.com/plan/5e36b5b82fd1d661#plan) , I don't see any immediate problems () and the query runs fast most of the times. I have pg_stat_statement active, but these slow executions are never stored:

postgres=# select max(max_exec_time) from pg_stat_statements ;
-[ RECORD 1 ]----
max | 2286.040693

That is only about 2 seconds. Do I need to activate any setting for slow queries to be included in pg_stat_statement? I have log_lock_waits set to on, but no slow locks are logged. What else can be the cause of these slow queries?