Hello,
It's been a few months since I last tried the integration asset and I wanted to give it anoher try with the new 2020 LTS.
First thing that struck me is that pretty much any interactions with the editor, as soon as it's displaying a sbsar on the project window will freeze and trigger the "Hold On" loading popup with various tasks ; Application.Tick, Gui.repaint, OnInspectorGUI. And even got an Out Of Memory crash yesterday.
And another thing that I had already saw back in august last year was that textures still get generated with random slices ;

Unity 2020.3.0f1 LTS - Substance in Unity 2.5.4 - HDRP 10.4.0
All .sbsar from Substance Source
i7 8700K / 32GB RAM / RTX 3080 / Editor & Project on Nvme