I bought an used stock ender 3 pro off a friend for quite a cheap price because he was buying an 700 dollar printer, and have mainly used it to print off minis and battlemap props. So far my prints were great, just a few failures here and there due to leveling but I have noticed with my last three prints that the quality went down quite a bit and can see some errors in the layer lines (pic related). Anyways, what i'm trying to get at is to how to diagnose these types of failures and what can I do to fix them?