Electron/Photon: Port does not open in Particel Dev Serial Monitor

Troubleshooting
1

I am on Win 10 and Particle Dev 1.5.1 and use Serial.print for monitoring during development.
Port (COM6) shows up in Serial Monitor but does not open although opens fine in other terminals like Putty and Arduino IDE.

2

Continuing the discussion from Electron: Port does not open in Particel Dev Serial Monitor:

Same problem also with my Photon although port is COM4.

I hope somebody can advice on this.

3

There is no point in having this same issue in two threads.

You can set the COM# for your devices in DevMgr advanced port settings (you can ignore the “in use” warning if you have always ever one device connected at a time).