By looking at your photos, both aperture and light source might be the cause, I do lean more towards aperture issue. One way to test them is to flip the light source and see if the edge glow follows? for example, don’t move the film carrier but switch the orientation of the light source, put the film carrier back on the light source. Does the edge glow show on the other side? If yes, then the light source is the problem, if not, then the lens is.
I have a friend using similar setup but I don’t recall seeing this dark corner on his photos.
Also, mentioned by @SSelvidge , the uniformity of brightness on Negative Supply basic light sources (either CRI 97 or 99) is really bad. I opened one of these and it turns out only two LED strips are inside the panel (usually there should be 4, one on each side). The LED they used is Waveform Absolute series which is indeed good, however only putting two in there is not acceptable. The cost of the light strip, based on my calculation, is only 15 USD, with the case and everything it would only worth 20 USD. I strongly recommend returning the light source if possible. Tried swapping a few with B&H but still no luck.
I currently use Raleno PLV-S192, an video lighting but it has really good uniformity and CRI, full report can be obtained here: Kaiser Slimlite Plano vs. RaLeno PLV-S192 (Brightness Uniformity) - #13 by yunhao.jiang
EDIT: If it’s aperture related, usually the four corner will look the same. OP’s image doesn’t look exact same on each corner so I do also suspect the light source being an issue. I used to have similar looking pictures when I use NS 4x5 light source, swapped and never seen again.