Appreciate the follow up. Toggling this twoSided flag doesn’t help as you noted.
There was a discussion about this same topic a few years ago. e.g. see issue (1) in below link and I even tried setting depth offsets and depth-bits as user rdb suggested. Doesn’t improve my case.
Rendering and shading issues on OS X
I am using Windows 10 though. Makes me suspect I am not alone with a small percent of users facing this issue potentially based on graphics card. Perhaps writing a custom shader could help but I guess that wouldn’t be trivial for shadows.