Thanks! Here's an update: I've got in touch with the Astak support over the phone and the technician provided me instantly with the correct instructions on how to resolve the problem: basically update the firmware.
With that said, after the firmware update (to 1.12.10), this is an entirely different device! The power up is instant (though it brings you to the books list instead of the last page which I was reading, but that's OK). The whole UI responds much better, it's definitely much closer to my 5" EZ Pro, which as I've mentioned I love very much.
Thank you, Astak Support!