I have had the bolt on the cutter come loose, a cracked blade--no idea how I managed to do that--and if you're talking about the right handed Martelli rotary cutter--the Olfa blades don't fit it quite right which makes it wobble. It needs the blade with only a small circle in the middle--not the kind that is a circle with tabs.
I have also had a lump in my cutting mat from fleece and flannel cause wonkyness (new quilting word--LOL). And cutting mats that are just crap--they have a rough, pebbly texture instead of smooth & slightly rubbery.