Thanks for the post Dodger but I was already doing that as I followed the instructions given here
https://www.mobileread.com/forums/sho...d.php?t=193184.
My problem came after I upgraded my Kobo Touch firmware to version 3.0.1 through the Kobo desktop.
As I use the portable version of Calibre, it was easy to do a couple of experiments such as removing calibre, and the books on my eReader, resetting my Kobo to factory settings, etc.
The upshot of it all is that it's now working perfectly. I don't have the KoboTouchExtended plugin installed but I have disabled the Kobo Reader Device Interface (2.16) by Timothy Legge and David Forrester plugin but left the KoboTouch (2.16) by David Forrester (which, incidentally, supports kepub files).