Sudden increase in connections in pgpool usage environment

Hello,
Thank you for always providing the convenient pgpool service.
We really appreciate it.
*This email was created using automatic translation from Japanese.

At the moment, we have no idea what the cause might be,
but we are experiencing a serious issue in the environment where pgpool is used—
sudden spikes in the number of connections to PostgreSQL, which is causing us great trouble.

The environment is as follows:

Server 1: Tomcat / pgpool (4.2.1) / PostgreSQL (13.11)
Server 2: PostgreSQL (13.11)

• A custom-built web system is running on Tomcat.
• The number of connections from Tomcat to pgpool is capped at 300.
• pgpool is used to provide redundancy between the PostgreSQL servers on Server 1 and Server 2.
• There is only one database running on PostgreSQL, and only one user connects to it.

In this setup, the number of connections, which is usually around 25,
suddenly increases to 100, 200, and even up to the maximum of 300 in just a few minutes.
This phenomenon occurs irregularly.

We initially suspected an issue in our custom system and ran pg_stat_activity to check the "query" column.
However, only a few queries appeared to be issued by our system.
Most of the entries were in the "idle" state after executing a "DISCARD ALL" query.

We suspect that some setting might be triggering a mass reset of connection,
but due to our limited knowledge, we are struggling with the investigation.
We apologize for the trouble, but if you have any insights, we would greatly appreciate it.

We apologize for the trouble, but if you have any idea what might be happening,
we would greatly appreciate your insight.