That last pic is about as great as it is confusing…
For once it is a bit cooler here, so I tried printing some thin patches with the door open.
All came out nicely, so no help.
Looked at the pic again and thought Whiskey Tango Foxtroot - makes no sense.
The top infill is diagonal, so if it is a movement problem the defects should appear with the fault, not in such a large and uniform area.
It IS a shot in the blue but could you print something small and thin just in the rear area of the plate and observe it from the from the first layer onwards?
Try to set the bed temperature to the upper max for PLA, like 60 to 65º Celsius.
It is rare abut if your bed heater is faulty it might just heat up this weir looking area.
A little FLIR camera would be really nice to check if the bed heats up evenly.
Just curious but did you try some higher temp filament for comparison already?