Windows Particle ID serial monitor disconnects on connect

I am remotely trying to help a developer diagnose why when he presses “connect” on the serial monitor in the Windows Particle IDE that it disconnects immediately. He can connect successfully via the particle-cli and via putty but not the Particle IDE where it always disconnects immediately. Are there any known issues or things I can suggest he look for?

Has he got the correct COM selected in the dropdown?
I sometimes have to select another COM and then select the correct one again, to actually have Dev take the one that’s displayed in the dropdown.

Could it be that another device has got hold of that COM at the time?