I'm a novice BN-20 user of 3 years. Those appear to be black nozzle deflections. I'm told it can be from a head strike(s) or nozzle blockages, possibly old ink. Mine had the same problem but worse.
I tried several head soaks to free unclog the 50 blocked nozzles. Only about 2-3 came back. I had to replace the head. Hopefully your solution is easier.