Hey all. New here and love the site. Just great contributers here.
This is just a thought, but this looks and sounds incredibly similar to what happened to a friend of mine. He has a Canon 70D, and about 5 months ago, he started getting these unusual spots just like the black ones. He did a manual sensor clean, but to no avail. He still had the spots, and even developed more, and it tailed off. So in some shots, the camera performed reasonably well, but depending on the lighting it started to really drive him nuts, so finally he sent it in to get serviced.
At first they thought it was salt air contamination, but it actually was excess lubricant from the mirror assembly. It wasn't a lot, but what they told him was they apply a grease type lube at assembly that generally stays in place, and almost never causes a problem, but sometimes some can migrate (like in warm temps), and it can actually flick off during operation if it migrated down far enough, and contaminate the sensor in the form of tiny spots. It actually takes quite a bit of care and effort to remove as it is designed to really stick to the mirror's mechanical joints. Anyway, they cleaned it up, sent it back and all is good. On your pics, they actually appear very similar. More organic and sporadic in size and like yours, there almost seems to be a little directionality in some of them....different than a pixel related issue, and there is the same almost haloing effect his had where the lube appears to leach from the center of the spot.
Not saying this is the definitive answer, but thought I'd share.
Good luck with your camera. Hopefully it's a simple inexpensive fix.
