My best guess would be too much butter. I have reduced the fat in my recipe over the time to the bare minimum and don't have many problems with spreading since. In about 80% of the times the cutter still fits on the baked cookies. And I don't re-chill / freeze my cutout cookies before baking.
I only have problems with shrinking sometimes. About the third time I roll out the dough, some cookies are smaller after baking... but this is a completely different story.
And yes, it could also be the different flour, different butter, new oven, or a mixture of everything together. Flour, eggs, sugar - they are all natural ingredients and differ slightly not only from brand to brand, but pack to pack. So I normally adjust the amount of flour to the individual batch I'm making. Sometimes a little more, sometimes a little less, until the dough has the consistency I want.