Great prints then suddenly terrible quality I've been printing with my Ender 3 for a while now and it's been great. I've had very few problems - depending on my settings, these are my typical first layers:



However with no settings or temperature changes and attempting to print the same files, I am now getting this issue with every print - The lines lay down and adhere fine, but if I watch carefully it looks as if the nozzle is causing the previous line to lift and warp. I have checked belt tensions, calibrated all axes.


The prints come out fine in terms of dimensions - all within 0.1&nbsp;mm overall size on large prints - but the quality is now terrible. I'm using the same roll. Prints were back-to-back and humidity is at 20&nbsp;% in the room I store and print in. I've checked the nozzle, checked the belts, tightened everything, rest the printer settings and put them back, regenerated the G-code with multiple slicers... I'm at a loss now. 

Any ideas, thoughts, comments, etc would be greatly appreciated.
After watching it countless times, I found out that it was the magnetic mat on the bed that has worn out. It no longer adheres to the bed completely flat and some of the texture was worn down more than in other areas. It wasn't visually detectable - I found it by checking the nozzle height with various feeler gauges in multiple random locations.