There are dark spots in the sky in the Western Montana landscape shots right before Cooper's doppelganger pulls his truck into the garage. They remind me of frozen versions of something called 'the blue field entoptic phenomenon' or 'Scheerer's phenomenon' which is a visual that sometimes occurs while staring at a bright sky and is caused by blood vessels rushing through your eyes :  https://en.wikipedia.org/wiki/Blue_field_entoptic_phenomenon

They could also be hinting at UFO's/aliens??

There seems to be an increasing amount of subtle alterations to reality occurring. The time jumps, the looping, reflection glitching etc. all seem to point to the possibility that reality itself is starting to come apart at the seams... "They are in our house now..."