In future, you should report issues with a plugin in the
thread for that plugin. It's only chance that I even saw this thread--I don't check the forum list very often.
You'd think that how covers are coded in epubs would be standardized, but it's just not.
Rather than attempt to keep the cover (X)HTML from the original, EpubSplit is coded to always use the same cover.xhtml code.
If your particular reader doesn't like that cover code, I'd try Calibre's Polish Book feature and see if it helps.
UPDATE: I see some kind mod has moved us.