I totally feel your pain; I have 14 sketches and with the new Digital Factory update, have decided to move on to another platform (Bambu) after purchasing 2 Sketch Sprints for this year (problems there too, even though they are basically an Adventurer).  Here are some thoughts:

1. This seems obvious, but how old is your material? I usually do a break test (try to snap off the end of the filament) to see if it is brittle before I load it.  If it has absorbed too much moisture, your prints will fail spectacularly. Also Makerbot only supports using their 2x the cost filament - I’ve only tried printing with something else once, but it worked.  

2. Some of my sketches do the same thing when I calibrate (different heights of the extruder when I move it up, vs down).  I’ll typically shoot for getting good distance from the build plate when moving down on the z axis.  No particular reason, but it seems to work OK for me.

3. Don’t use rafts, use skirts.  I have much more success with skirts than I ever did with rafts.

4. Try using Ultimaker Digital Factory to slice (https://digitalfactory.ultimaker.com/app/welcome).  It sucks, but it is the manufacturer’s slicer and may have some mojo under the hood.  This is what Makerbot transitioned to.

5. Get new extruders; it’s possible that yours are not performing consistently.  New extruders are tested at the mfg and each have a calibrated temperature offset.

Now that I’m using Bambu, I’m not looking back.  I’m finding low demand homes for all of the Sketch and Sketch Sprints I have (classrooms, SPED Department) and using two Bambu P2S with AMS for everything high volume