The 2 and 13 second events certainly look different! It is hard to say from this video. I would be disappointed to see that on my machine as well. My machine is less than perfect and has considerable backlash, but I do not see this jumping while cutting either way. Catching debris under the cutter can cause some cutting problems. Lubricant can help. I have a CNC machine and there would be no way to lock down the the position and still cut a circle, arc, corner turn etc. So tighten your gib up until you just start to create backlash. Looser and the way parts can move about. Any tighter and backlash starts to be a problem. This is the correct gib tightness anyway to prevent twisting (maintaining 90 degrees between x and y). This jumping should not be the bearings, if they are that loose you have more to worry about. If your spindle head or table is light weight or the structure is not strong then maybe the mill "bends" when it hits a strange spot of cutting. Or maybe the spindle motor takes on a sudden load and slows a bit. A thought, one way to check on weigth is to add weight to the table or to the head so that its inertial/momentum is larger. Lastly, you have a quill. Make sure that it is locked down. Some quills have considerable looseness and so the spindle can effectively move about. It can be bad enough on some machines that drillling holes are not located where they are suppose to be. When I want to use the quill I tighten it up to where it is a bit difficult to drive. I never leave it unlocked while moving in x or y directions.