3.
Are the white halo on the sides of the image caused by stand development? The background was white but had some distance from the light used.
View attachment 367395
The image in the centre (1600), aside from showing density variation artefacts like the other ones, shows bromide drag artefacts on the left border: you can see a repetitive pattern of uneven density whose spacing is compatible with the sprocket holes of 35mm film.
Bromide drag is a by-product of reduced or insufficient agitation techniques. Bromide forming during the development process slows down the development where bromide collects. Bromide will collect in or around sprocket holes and run down the surface of the film causing the streaks that you see in the middle frame.
The above is not the effect of scanning: I know of no scanner sensor that can produce the patterns in the centre image. It's the effect of your development decisions. You didn't say what you're using to develop. If you're using Rodinal, my personal experience is that it works much better for 99% of the scenes I photograph diluted 1:50 and correctly, and regularly inverted once per minute. You only have to do it for 7-10 minutes, it is not a lot of work, and you'll be rewarded by negatives free of bromide drag and nasty (IMO) border density gradients like the above.
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EDIT - I have now seen your negatives: the density effects you experience are being exacerbated by the fact that your negatives are overdeveloped for scanning. Your dynamic range is extremely low, and the scanner software will (unless you defeat it) try to expand that compressed signal and stretch it to utilise as much of the available bit space as possible. This means that existing density differences in uniform regions of the negative will be more noticeable in the scanned positive.
So - if you plan on avoiding the above - on top of moving away from stand/semistand and using 1:50 dilution and regular gentle inversions, also work on optimising your development time to achieve lower highlight density than you see here: all that density is not needed and it's in fact holding you back, if your purpose is scanning