Problem using 4 USB ports at the same time: "could not open port"

[Melek-Cherif]

Hello,
I am encountering a weird problem with my RPi communicating with 4 esp32 via USB serial communication. When using 3 or less esp32, the system works perfectly, but once I tried to use 4 ones at the same time, things got messy.

The system consists of an IoT device where the raspberry handle receives messages from esp32. So the code lists the ports and sends for each one of them a start message to start sending data once and then waits for the next start message.
At first the system worked for 2 or 3 cycles, then the transmission got slower (the transmission time went from 2 seconds to more than 12 seconds), and after that I received the error that I couldn't open the port as if the esp32 was not plugged. And it persists until I reboot the raspberry.
I think that there is some problem in the traffic of messages and an error accumulation that ends with shutting down the port. Also, I checked the power supply and the power delivered for every port, and it is sufficient and should work. I think there is something missing in the logic of transmission.