Raytracing "area" lights causing artifacting - 2 different, possibly separate, issues

Edit: I realise now that the embedded pictures have come out tiny - please click on the thumbnails below the post to view fullsize. /Edit

I have a scene I’m trying to render using soft shadows. For this I’m using several lights, all of which have a soft shadows setup. I’ll discuss each issue separately:

First Issue:

(apologies for the small images/flat pink shader - I can’t show any more than this, and can’t reproduce the issue quickly enough to make it worthwhile)

The issue here is the grey “halo” around the edges of the asset silhouette - it is NOT a contact shadow as you can see it lightens the area around the part marked with an arrow compared to the shadow beneath.
It manifests when using an area light with a non-zero source width/height and multiple samples per pixel. The grey halo gets darker as you increase the samples - These images captured with RTX reflections, GI, AO all disabled. If I move the area light the dark-halo can disappear once it is close enough to the light - you can see it “rolling” down the silhouette edges as you bring the light closer. As you can see in the image, the effect worsens as you increase the number of samples, but seems to cap at around 8 samples I believe.

Second Issue:

The issue here is the banding, almost hard lines or edge-loops, happening towards the edge of the shadows. There is the main, hard, dark shadow, and then multiple lighter shadows around the outside of the main shadow, that follows the same shape.
The issue manifests when using point lights with a non-zero source radius and a non-zero samples per pixel.

  • As you increase the samples the problem gets worse, but (possibly?) seems to cap around 16 samples/pixel I think.
  • With a larger light source-radius, more lines appear in the shadows:

Unfortunately, due to the requirements of my project, I’m having to use quite large source-radius/light-width/height and high numbers of samples - the denoiser is not working well enough at this stage to clean out the noise caused by my lights, and my shadows have to be soft, so the situation arises where I have to pump up the numbers - however I then run into the issues raised here.

If anyone has any ideas how to solve this, or has experienced/recognises this themselves then please let me know.

UE 4.22.1
NVidia 2080 @ driver
Windows 10 v.1903