Testing out the 5.2.1 Remove Module with a very simple video, a dog wandering around on some sand, and I'm getting some weird results.
Plus the interface is slightly hiccupy.
First the problem. With Illumination:None, Randomize, Dissolve Width: 8 no 3D, No Flood Fill it does indeed produce a speckled 8 pixel boundary around the object being removed.
But as that look pretty bad I selected Blend with the same Dissolve Width: 8. It doesn't dissolve, it just expands the area that it replaces, with a very visible hard edge between the replacment patch and the area outside it. All values of Dissolve Width from 0 - 100 do exactly the same thing (although 100 grabs some data from nowhere in the video and puts a big splodge in the middle).
Different value of Dissolve Width in Randomise mode do produce larger speckled bands around the replacement area, so it knows where it should be doing the blending, it just isn't doing it. If it did dissolve, or blend between the two varying lighting sections - as the docs say it should - the results would probably be acceptable.
I added 8 to the Edge width of the object to be removed and retracking the background, thinking this would mean it would use the alpha channel of the object's mask to fix the problem, but that made no difference. It was just like enlarging the Dissolve Width. The area replaced was just larger, but still with clashing lighting and a hard edge. The alpha edge of the Object to be removed had been ignored.
Next option: Linear. That produced a very blurred patch with almost no contrast that looked nothing like anything else on the video. It also has a hard edge (despite using an increased Dissolve Width of 12) between this blurred patch and the surroundings, so looks worse than using None in every way.
Interpolate produced a better matched result in terms of colour and contrast, but it had hard edges around smaller patches inside the removed section, which it had made up from several other sections. This was despite it again having a Dissolve Width of 12.
Changing to Randomise with the Dissolve Width of 12 and Interpolate: the little internal patches then had dithered lines around them, which highlighted the patchwork nature of the section it was using to make the replacement.
So, with Blend not working with any of the Illumination models, it makes all of them either have hard edges in or around them, or the randomised dithering, in or around them.
Deleting All Keyframes for the various settings using the (x)ALL button after selecting them and reply yes to "Delete all Dissolve Mode Keyframes " etc. does not delete all Dissolve Mode keyframes. Despite a Blue box highlighting the entirety of the Dissolve Mode area, including the Width, DissolveWidth has its own keyframes. Which need to be deleted by highlighting the actual number itself, then (x)ALL to get the "Delete all "DissolveWidth" keyframes" popup. That still doesn't work, as despite no keyframes showing, 'ghost' keyframes still appear in the Dissolve Width box when on certain frames of the video and have to be overwritten manually to the same value as those either side of them.
Also, despite the Blue 'selection' Box highlighting the entire Illumination Model area, (x)ALL on that does not 'Delete all the "IlluminationModel" kayframes' because the Smoothing level has its own value "InterpolatedSmoothingLevel" which must be deleted by selecting that value directly first.
3D Compensation , Flood Fill do not have a Blue selection box around them, and they must be selected separately with (X)ALL as 'Delete all "Use3DCompensation" keyframes' and ' 'Delete all "UseFloodFill" keyframes' individually.
The Flood Fill Smoothing Level value has its own " 'Delete all "FloodFillSmoothingLevel" keyframes', although both it and the Illumination Smoothing level values were often greyed out and inaccessible, despite Interpolate or Flood Fill being selected when they should have been active. One way to make them responsive seemed to be to start to remove a frame, then cancel it, when the removed object would reappear and both Smoothing Level values would become accessible again.
If Blend worked as advertised and the keyframes were actually deleted, then I'm sure the results would be better and it would be less frustrating to use.