There has appeared an area darker than the rest, after an hour of development in rodinal 1:100 at 20 degrees, agitated (inversion) for the first 30 seconds then for 10 seconds on the 20/40/50 minute (stopped: 20seconds, fix: 2 minutes), the negative developed well and mostly uniform except this one area about 1cm right along the one edge of the film.

is this caused by developer sinking to the bottom of the tank, or not enough fixing, stopping, developing?

I've attached a scan of one frame for everyone to have peak at, some are more prominent than others and on one frame looks like waves (too much agitation)... so I'll stick that one up too.

thanks in advance

Ilford (7).jpg Ilford (12).jpg