Chrome Version       : 54.0.2840.99
What steps will reproduce the problem?
call navigator.requestMIDIAccess({sysex: true}) in a webpage script

What is the expected result?
After leaving the page without using the MIDI ports, they should be free to use in other applications. Also after using the MIDI ports and calling .close() on them after sending/receiving data, they should be free to use in other applications.

What happens instead?

The ports are locked. When trying to use them in any other Windows application, the error occurs "There is not enough memory available for this task...." This is known to be a confusing Windows error shown whenever a MIDI port is being accessed simultaneously from 2 applications. 
It is impossible to unlock the ports by closing the browser, by disconnecting/reconnecting the USB-MIDI interface, by changing the Chrome settings to reject MIDI access. The only way to unlock is by rebooting the system. After that MIDI ports can be used until they are accessed by Chrome.

This only happens with class-compliant MIDI-USB devices (without device specific driver installed)

OS : Windows 10 Home 64-bit