It seems that you have made some modifications in the registry related to USB serial settings. Could you please export the registry keys HKLM\System\CurrentControlSet\Control and HKLM\Drivers\USB\FunctionDrivers? for both cases: the working T20 and the problematic IMX6.
Please also try solution listed here - Can we access the virtual COM port using COMx rather than \\.\wceusbsh001? - #30 by raja.tx