Try scaling up your Area lights. They are probably at the default size of 1x1. I usually start at 4x4. You might also want to switch over to Physically based attenuation for each light as well. Change the Mantra node to Physically based too!
Using Houdini Indie 20.0 Windows 11 64GB Ryzen 16 core. nVidia 3050RTX 8BG RAM.
it's the size of the lights. Increasing the size fixes the shadow issue, of course now it's a matter of tweaking intensity/position/rotation in order to keep the same kind of result.
Edit: although, now that I'm thinking again about it, as a 3ds Max user I used this trick to get the type of shadow I needed. In other words, if I want a kind of harsh shadow, but still using area lights, I simply make the lights smaller and I increase the intensity. In fact right now my shadows are softer, which makes perfectly sense. There must be a way around in Houdini then, in order to get the same of type of shadow yet avoiding the edge overlay issue. Maybe using another light for shadows only, which probably is the Phantom option, but I can't find any render tab options for the selected light.