some sort of extruder issue  

some sort of extruder issue

Hi everyone I have done a good deal of printing over the years but have not seen this issue before. This MK3s has a good number of hours on it but generally works with one issue. It builds up a blob that then attaches to a print and causes a crash. We are printing a bed full of these parts and within the first few layers you can see what happened. 

I have noticed that the extruder loosens up over time but I have retightened it without change in the issue. The machine is newly calibrated, the rough print bed is clean (washed in soap and water and not touched). I didn't slice the part but I guess they are using the default settings for Prusa PETG, .4 nozzle and .2mm layers.   The nozzle could be getting over size but only printing petg and pla I think the wear rate should be rather slow. 

thanks

Luke