Are you sure no towels got in with them? Or fleece?

Are you using a communal building machine or a personal one?

This happened with our old top load water hog washer. The repair guy pulled out what was more or less the lint filter of sorts ( IIRC the tub was removed first? It was maybe ten+ years ago ) and we both chipped away at a 1/2" thick layer of years of undissolved powdered detergent buildup ( probably from teenagers doing laundry and cold water washes) and maybe even lint. That did the trick.

I would buy a lint brush or two or three, use it until the lint is off, and then wash these blacks by hand in a bathroom or kitchen sink. Even though the maintenance group said they took care of the machines, who knows what they really did, or if what they did solved the problem. Well I guess we know it didn't solve it, so better to do these by hand.

I don't usually use fabric softener, but I keep a package of unscented sheets (because I can't tolerate the scented) and use it when this happens. It seems to reduce the ability of the lint to stick to the clothes. I also sometimes throw a dark colored towel into the dryer along with the softener sheet.

Also in the future, turn your darks inside out before washing. Any lint will end up on the outside (insides, really).

Be sure to empty the lint filter in dryer before drying.