I use Linux with the nRF52840DK. I have three such developer boards, and only the one with the serial number 1050205291 exposes two ttyACM interfaces on Linux vs the other two boards with the serial numbers 683150769 and 68350417.
The processor of the 1050205291 board on which Segger runs is visibly smaller than the other boards, which might explain the difference.
In some situations, the two ttyACM interfaces are useful, so I'd like to use both on all my boards. For example, the "Bluetooth: Central UART" demo utilizes a ttyACM interface for logging and the other for communicating via UART.
Please let me know what causes the difference and how I can make all my boards expose two ttyACM interfaces.