Hi there
I had exactly the same problem on my D160R - the cuts wouldn't meet up when cutting letter 'O'. Both the inside and outside cuts would have the same 'notch' in them. Sometimes it also happened on the round parts of 'd' and 'p' as well.
Loads of suggestions for it were made by Summa and the machine's installers (it's only 8 months old!) - from the media being too thick, to re-calibrating, and even to use a Sandblast blade and holder.
The best and only solution to it that I've found is simply to put a nice new blade in the cutter! (Not the sandblast - I've never got that to give a decent cut! Awful thing!)
The new blade seems to cure the problem for a while!
If you come up with any other solution, please post it! I'd be really interested to give it a go myself!
All the best.