Repeated print failures with Ender S1

Hello

A week ago, I repeatedly failed a particular print for a ball joint. It would print about 1cm+ and then build up material which the nozzle then would run into. I tried many different variations of PLA materials, temperatures, support, orientation, wall and infill settings. It failed every time, but never at the same spot.

Other prints would mostly work, but a few failed which I attributed to a lack of a proper adhesion to the print bed - old PEI sheet that needed cleaning.
Unfortunately, the failures caused plastic to ooze out of the nozzle and the bed was pushed around so much that the adjustment wheels fell off.

I upgraded the hotend to a 300C version and cleaned the entire extruder. I re-levelled the bed and replaced the PEI sheet. Adhesion was working better.

However, prints were still failing. I noticed that the printer was slowing down after a while, causing material build up. I reinstalled OctoPrint on a new SD card which seemed to fix that particular issue.

Prints with PLA and TPU on the new setup worked fine, including a 11h print. However, the initial ball-joint print still fails.

Printing a Benchy, it seems that the nozzle gets closer to the print as time goes by. Initialy, for the first few layers, it's at the seemingly right height, but then starts touching the print after 5mm-10mm

I'm out of ideas.

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