Calibre has evolved and the Plugin code (for many) has tried to keep up, so it is not unreasonable for OLD code to fail.
as to 'Watch covers"...
Sorry, but they only show when selecting or first opening a book. so why? I am not using my 2010 Astak which only had 1G

of SD card space (with room for more books than I could read in MONTHS) any more.
My 4G deviced have almost 100 books (with covers) and are not half full. (True, I use the
Resize Cover PI and make mine 450x680 for a 600x800 display since Photo Quality is not something Eink needs)