If the mixer is being pushed to its limits or has too many high-draw phantom-powered microphones plugged in, the power supply works harder, generating more heat [Source].

Would you like detailed thermal modding instructions for the most likely candidate (NX series amp) or the tube preamp?

: Some users have reported connectivity and power fluctuations when using high-speed USB 3.1 Gen 2 ports, which may contribute to irregular hardware behavior. Recommended Troubleshooting Steps Check the Cable

Decoding the Buzz: Why the “Behringer N11999 Hot” is Breaking the Internet