Bad print Quality on Z18

Hello community,I got here 2 Z18 (and sadly I cant do anything about it so I have to live with them) and they worked fine until some weeks ago. Now one of them makes really bad prints. See attached images. The other one works fine! We already tried follwing steps without success1. Fasten the belts2. Running calibration3. swapping smart extruder4. changing NEMA17 (for extruder)5. using different filaments6. changing extruder temp.7. Downgrading to old FW8. upgrading zu newest FWWhatever we do.... one of them prints bad, the other one fine. The only thing we didn't do yet is swapping the controller but this will be really a pain in the ....maybe anyone has an idea what else to try?We are runnung the latest makerbot print und FW but the bad prints also happens on the internal calibration cube :-(thank you for your help!!!