Problem with my prints

[vanias78 0]

Hello i need a little help.

In my last printings the printer started to make problems on the first layers.

Problem in corners.

Also the down layer is not smoth as was in my first prints and there are holes on it.

[vanias78 0]

i cant understand what is this black on white filament. I made 5-6 prints. I tried cleaning it with ultimaker method. Prints white and suddenly i can see this black spots in diffirent places on my print.

[Nicolinux 288]

Hm, that's really hard to say. But since you have an UM2+, do change the nozzle and print again. If it happens again, you could exclude the nozzle from the list of possible causes.