It looks exactly like bromide drag.
Bromide drag happens when you don't agitate ENOUGH when using a developer that is made to be agitates. It can initiate from high density areas of the film and drip down from there (in which case it will be uneven looking), but it can also initiate from the sprocket holes, in which case it will look exactly like this.
One solution is simply to agitate a more than whatever you're doing, and thus not give the bromide enough time to drip down your image and pollute stuff. Instead it gets agitated away harmlessly into solution before it builds up enough to drip.
There's not really such a thing as "too much agitation." There are methods where you in fact constantly agitate for the entire development time (like BTZS tubes). The result of more agitation is going to be not a ruining of your photos, but instead:
* Less shadow detail / higher contrast
* Faster developing times
Another solution is to switch to a different developer. If you don't want the higher contrast that comes from more agitation, but you also don't want bromide drag, then get a developer that is designed specifically for low-agitation, long term "stand" developing or semi-stand developing. The classic example being
Rodinal. Or
HC-110 is a little easier to find for sale. Other options include pyro developers (like
pyrocat HD), or homemade slow developers like
obsidian aqua, or coffee-based
caffenol developer.
The reason those streaks are in such straight lines is the developer is being churned through the perforations in the film...take a look...the streaks are RIGHT in line with each perforation on the side of the film.
I disagree. This would not lead to straight lines. If it was violently squirting through the sprockets, it might lead to uneven development, but it would be in the form of circular or very diffuse elliptical at most "halos" of differential developing, not perfect straight lines. Straight lines mean drips, not violent squirts. And drips mean bromide drag.
Combined with his statements above that he has been intentionally doing less and less agitation, the opposite (sort of) problem of bromide seems the better fit.