Agitation technique troubleshooting - Insights needed

Hi there.

I'm trying some new agitation patterns with Rodinal 1+49, as I've found that reduced agitation tends to yield better results, tonality-wise.

Yet, I'm getting these vertical streaks. The faint, overdeveloped ones in the "middle" of the frame actually appear on the negative.
The darker ones, close to the edge, very straight and more "defined" seem to be a scanning issue, but I'd like to have some point on that as well, even though it might be OT, since I've never had such a thing happen with this scanner.

As I've stated above, I'm using Rodinal 1+49, 20 degrees C. Timing here was 21 minutes, paterson tank with 600ml of solution. Agitation was continuous the first minute with the twirling stick, then 4 inversions every 3 minutes.
Ilfostop and Ilford Rapid Fixer for 6 minutes. Ilford wash sequence and a further sitting in distilled water with Ilfotol wetting agent.

Any opinions and suggestions are greatly appreciated, thank you

What format is it? If it is 35mm, I have had the same streaks (emanating from the sprocket holes) in deep tanks, which I suspect was cause by agitation that was too gentle. I was trying to be super careful to prevent such a thing, and I may have cause it instead.

It's 120. And the streaks are in a direction which is horizontal, respect to the tank. That is, they are parallel to the counter top. They are vertical only if you consider them while the negatives were hanging to dry. I doubt they might be drying marks, but I can't sort the option out completely...

I've also had trouble with uneven development with Rodinal. I dialed my agitations way back and still had sprocket marks in the frame. I eventually figured out that how you agitate is more important than how often. Slow, rotating inversions followed by a spin on the counter did the trick. My plain old inversions were not random enough.

600 ml of solution sounds like too much. 600 ml is about 20oz. I use a 16oz stainless tank and for the longest time I'd fill the tank up to the brim. I would occasionally get streaks of built up development along the edges (but no sprocket streaks for 135 film). Plus I would also use very slow agitation. Finally it was pointed out to me these mistakes. Now I use 400ml of working solution for 120 film. This just covers the reel but allows enough space above for increased turbulence for even agitation. For 135 film I use 250 ml with the empty spacer reel on top. Again, this just covers the reel. I then increased my agitation to five inversions every 30 seconds after a full 1st minute of agitation. My negs look so much better now. I use Rodinal 1+100 but I've had similar issues with HC-110. So make sure you are not filling your tank to the brim. The solutions, including fix, need room to slosh around in for even development.

Thanks marcmarc (end everyone else here!). Actually with a Paterson tank 600ml is just 100ml more than the prescribed 500. The tank isn't full this way, and with 500 I often had "bubble" overdeveloped signs on one edge of the negatives.
If I agitate 4 times every minute the negatives are perfect: the problem comes when I tried agitating in 3 and 5 minutes intervals. Last time I tried with 2 minutes between agitation and it looks like a good compromise; but still have to print something from that roll. I'l keep you posted.

Cheers.

Second Matthew's suggestion about using gentle tank rotations. I found with Rodinal 1:100, semi-stand similar to your scheme, I do 30 seconds of agitation (you read right, 1/2 a minute) of very slow, gentle twist inversions every 4 minutes, after an initial 2 minutes agitation after pouring developer in. The length of time is to ensure a complete change of chems, and the gentle movement prevents edge surge and other directional patterns.
I also measure just 20 - 25cc more than needed to cover the reel, and no more, to ensure adequate room for the chems to move about, important.
I've been working at this for 3 years, and this is my current prevailing method. I have this problem with no other developer, but I like the results, so there you are.