I agree, it does appear to look like the result of bubbles. However, I was not sure since none of the other photos on that roll had this issue. It was the upper roll, both rolls were pressed firmly down into the tank and onto the spool holder, they were covered in plenty of solution that I could tell.
I know I had plenty of Diafine in the tank to more then cover both rolls of film, but I am wondering if maybe your mention of over-agitation may be what's the culprit.
With DD-X, I always did 10 "flips" of the tank at first, then 4-5 each minute during the process. With the Diafine I typically do 5 to start then 3-4 per minute. However I noticed lots of bubbles this time which I've not seen before and I think maybe I got a little over zealous with the agitation.
My Diafine has only had maybe 10 rolls run through it, so it shouldn't be bad/used up yet. I've read folks using the same batch for months or a year without issues.
I have 2 more rolls to do left and I think I will try to do them using the very gentle agitation instead to see what happens. I am hoping it was just me going a little to aggressive with the tilting of the tank. I did have my mind elsewhere since I had used a broken lens and was not even sure if there was anything worth saving on the rolls. I had way over and way under exposed a few shots just to see what would happen and I got all my shots well within tolerance and adjustable after the fact. So really the only issue I had was that bubbly mess.
I also am very good about the tap of the tank on the counter after each agitation. I had that drilled into me by dozens of how-to and threads about self-developing. So I am going to go with bubbles. AND, the fact that I had, lets say, some issues loading the film into the roll and I had 2 places wehre the film sat wierd. I wonder if the bubbles got trapped there and couldn't diffuse or rise up and out in that spot. I know had one other place where the image had a white spot from where the film touched another piece of film.
I love the nearly instant reward of doing my own development but I am still learning this process, again. This time, unlike when I was a teen, I am doing so with my own money and equipment. It's quite a wonderful feeling.
Even the mistakes are fun, I learn, grow, and get some cool ideas for things to try later.
Thanks for your input!