Heat creep it is then!! Glad it’s better. Squirrel cage fans are the way to go
Heat creep?
I agree with Griffin on the fan thought.15x50mm or 30x75mm depending on your config.
Google heat creep 3D printer.
Yes, it’s available as a filter but most cameras are darker around the edges (vignette) although most now control it enough to not be noticeable. It looks to me like a phone camera shot with the LED flash lighting up the centre of the shot more than the outsde and giving the change in colour. across the frame.
If you can, try taking the shot again under natural sunlight without a flash. This way those who know printers well (not me) can have a better chance of working out what’s going on.