Welcome to Hero Machine. I also use a Mac and was having trouble with HM3 when I first started. Are you using Safari as your browser? When I started with HM I could only use HM2.5 and HM Classic on Safari. I added Google Chrome and have no problem with HM3 now. Hope this helps, good luck.
I’m also on a mac and I’ve never had any of those problems, using Safari or otherwise. Some weapon items can only be found in the items-right section. Don’t both looking in items-left because it only contains the tech & horror items.