Why does QGIS creates multiple connections for PostgreSQL Server?

Question

We have a PostgreSQL database with PostGIS running and today we ran into the issue that too less connections were available. Mostly we are using QGIS to access the database. We realized that issue because multiple users got the following error:

FATAL: remaining connection slots are reserved for non-replication superuser connections

When checking the number of connections in pgAdmin I realized a thing I saw before, but as I never ran into problems didn't care too much about.

QGIS creates multiple connections to PostgreSQL for the same user to the same database.

Now I am wondering why this is the case and how I can maybe change that behaviour.

Could this happen for example if a person got access rights to a database through different user groups?

One approach might be the issue that some users run into that if you add layers to a QGIS project that was created before might ask you multiple times for your login credentials if those changed. This seem to me that probably different credentials are saved with the project and therefor multiple connections might be used. Can anyone confirm or dispruve this? - Suggestions for a test scenario are also welcome to check this.

Any ideas, hints or soutions are welcome.

By the way: Yes we increase the number of max_connections, but I want to understand why this happens and get closer to the core of the situation.