I had the same issue and messaged customer support about it and got the following response, which solved the issue for me.
1. Download the archive with firmware at the following link
https://yadi.sk/d/DzTy9frJvnUGa.
2. Extract the content of this archive on your WINDOWS PC.
3. Connect your ONYX MAX to your PC and then switch it off by pressing power button.
4. Switch your ONYX MAX to the HID-compliant device mode. For this do the following:
a. Press simultaneously both keys PAGE UP and PAGE DOWN (with < and >) the lower left corner
b. Keeping them pressed, turn the power on by pressing the power button for about 2-3 seconds. Then release all the buttons. The eReader is in the HID compliant device mode
5. Run the program MfgTool2 from the folder which was extracted from the downloaded archive.
6. If everything is OK, in the first line of this running program you will see HID-compliant device mode
7. Press "Start" in the program and wait until the progress of installation turns from blue to green.
8. When the progress of installation becomes green, press “Stop" and
the "Exit" in the program window.
9. Switch the device on by pressing the power button.