Okay there is one configuration that can cause this issue unfortunately it's not mine.
Here is solution from Softube:
"I have re-created your issue here, but under some very specific circumstances which I would like to check with you: are you running Google Chrome?
Turns out that the default setting in Chrome is to access whichever MIDI port is available!
If this is the case, please do the following:
1. In chrome navigate to 'Settings > Advanced Settings > Content Settings'.
2. Locate the 'MIDI devices full control' section.
3. Enable the 'Do not allow any sites to use system exclusive messages to access MIDI devices' option.I have re-created your issue here, but under some very specific circumstances which I would like to check with you: are you running Google Chrome?
Turns out that the default setting in Chrome is to access whichever MIDI port is available!
If this is the case, please do the following:
1. In chrome navigate to 'Settings > Advanced Settings > Content Settings'.
2. Locate the 'MIDI devices full control' section.
3. Enable the 'Do not allow any sites to use system exclusive messages to access MIDI devices' option."