This is the included MySQL DB maxing out on the allowed concurrent connections. Normally you wouldn’t come close to hitting the maximum. I would assume there is some external factor here, like custom code, or a shared resource. If the hardware you have is supported, you could open a ticket.
I would recommend researching the below, then look into what is using your concurrent connections. You can then work to resolve errors, or if you find that the system is working as designed and you have the headroom, you can increase your maximum connections parameter.
Tracked down the database connections to a Google Cal link that was failing to connect to Google servers. I removed the remote calendar url and the mysql connections settled down to normal operating connections.