That looks like local poor adhesion, probably a greasy fingermark on the print-sheet. Time for a wash.
Cheerio,
RE: "Watermark" under print
Yes, the bottom left corner of the print detached. Besides bed cleanliness, this can also be affected by the shape of the print (as printed plastic cools, it shrinks, and this creates forces that pull edges off the bed), and also ambient temperature (cold air means the bed heater is less effective at keeping the plastic above the immediate surface warm).
Besides cleaning, you can also try using a “brim” in the slicer, adding “mouse ears” to your corners, or redesigning your part so it doesn't have sharp corners. Sharp corners that have walls above them have the greatest tendency to lift.
RE: "Watermark" under print
I never considered that it could be an adhesion issue. I'll try those suggestions next time I print a similar shape. Thank you for the tips!