I found the same. Got a 2.1 in my undergrad, but a distinction masters. I found the latter much easier, and much more engaging. Some people just seem to be better suited to it. At the end of the day, and undergrad degree is very broad, it's about narrowing down your area of expertise. Once you're doing a masters, you've picked - hopefully! - the one are that interests you above all others and have the chance to show off your knowledge and expertise over a greater number of words.