Hi
In case there remains problems with dual-USB operation you can take a look at the uTasker project which allows code to run on Kinetis and i.MX RT parts with single or dual-USB.
The following short video shows the same project running on a Teensy 3.6 (K66F with FS and HS USB) and on an i.MX RT 1060 with USB-CDC on the first HS USB and MSD host (memory stick) on the second.
The complete USB controller operation and memory stick are also simulated so that development and debugging becomes much easier and more fun!
No porting between parts is needed and dual HS USB runs on i.MX RT 1050, i.MX 1060 and i.MX RT 1064 in any combination: device + host, host + device, 2 x device, or 2 x host.
https://youtu.be/3irORtbc4e0
Regards
Mark
[uTasker project developer for Kinetis and i.MX RT]