Strange layer problems

[robsco]

From the included picture, what could be going on here?It's an Ender3 v2, I just did the exact same print which came out fine, but after removing the glass base to take the print off, and put it back, this happened.That's not a shadow by the way, if you see towards the right in the light, the layer has clear lines for some parts, but then it's as-if it's really flat.Could this be a dodgy filament?I levelled the base before the print, using the paper trick, and all was as it usually is before a print.I also noticed when it printed the skirt, it sometimes doesn't print at all in some areas - I can't see how it's a levelling issue since the paper trick was used in all 4 corners.Any advice or comments greatly appreciated.