Here’s a checklist for starters:
- Did you change the printing speed halfway through, by selecting Sport or Ludicrous mode?
- Did the part move on the plate halfway through the print? Wash the plate gently with warm water and dishwashing liquid (do not scour it), and apply some glue to the clean bed (preferably liquid glue)
- Is a cable snagging inside?
- Are there any loose screws, bolts, etc? Check systematically from the nozzle, to extruder, to gantry, to belts, to stepper motors (but I doubt that it is this, and the cause/solution lies above)