There can be many reasons for this. Either your temperature for the nozzle is too high, retractions are too long, or the front cooling fan is insufficiently cooling the heatsink. It may be all three but diagnose the machine for all three to be safe.
1. Lower the temperature of your nozzle by 5 degrees C increments 2. Lower retraction settings – for Bowden style printers lower it to 4mm and for direct drive style printers lower it to 2mm 3. If the fan is not working, then the inside of the hotend would be clogged (heatcreep) causing the filament to be stuck. Replace the fan.