When I plug the camera into a USB port on my big computer (not the little RPi where things work, now), I get this with dmesg:
[25194.576083] usb 2-5: USB disconnect, device number 6
[25201.620053] usb 2-5: new high-speed USB device number 7 using ehci_hcd
[25201.752439] usb 2-5: config 1 has an invalid interface number: 1 but max is 0
[25201.752446] usb 2-5: config 1 has no interface number 0
I am unsure what this "config 1 has an invalid interface number: 1 but max is 0" is about - but I think it is central to the problems I have.
I installed from source both on the RPi and now on the big computer - so I think the problem is not related to indiserver or indi-sx but rather to something about how USB ports are handled by Ubuntu vs the version on RPi. This is probably off-topic for this Forum. Not sure where to go with it: the topic "config 1 has an invalid interface number: 1 but max is 0" is unsolved but common if you Google.