cdc_uac2 (RPi Pico 1) but with three CDC ports - locks up after a few CDC port opens

[devzendo]

Hi, thanks all for TinyUSB!
I've started a project based off the cdc_uac2 example, but I want to extend this to an audio in/out interface (probably mono, stereo not needed), with three CDC ports rather than two. I've extended the usb_descriptors definition along the lines found in https://gist.github.com/todbot/d4f4e0111c7829fd55b0c3b68114d9a5 (show three CDC ports working in TinyUSB).
When my pico is connected, Linux (Mint 22) kernel log shows:
cdc_acm 3-1.4:1.3: ttyACM0: USB ACM device
cdc_acm 3-1.4:1.5: ttyACM1: USB ACM device
cdc_acm 3-1.4:1.7: ttyACM2: USB ACM device
I can connect to these ports with e.g. minicom -b 115200 -o -D /dev/ttyACM1 and this works, I can connect to a couple of these ports in turn (my code echoes the input along with the port name).. except after a few connections, the connection to a port fails, and minicom hangs. e.g. connect to port 0, echo text, exit. connect to port 1, echo text, exit. connect to port 2 - lock up.
Can TinyUSB provide an audio in/out with three CDC ports? I had to arrange the endpoint numbers differently from the above example as linux reported a conflict with the audio endpoints.
My code is at https://github.com/devzendo/onni/tree/main/src
Could anyone point me in the right direction please?
Thanks in advance, Matt.