17.3 icon themes don't work properly in 18.2

Using a custom theme developed in mint cinnamon 64 bit 17.3.
One specific instance is excessive changes to categories directory in the theme to make the menu change as well as software manager changes to icons.
The theme is placed in the users folder ~/.icons/ThemeName

Works okay in 17.3
In order to make it work in 18.x (now on 18.2) and also tested in 18.3, you have to put the theme in the /usr/share/icons folder. It only reads some icons if installed in home directory, but all icons including the categories work in /usr/share/icons.

The theme is built on the folder structure of: 8x8, 16x16,24x24 etc to 256x256 folders then subfolders in each like categories, places, mimetypes etc. All images are PNG. There is one scalable folder with devices and status subfolders and they contain svg images. I tried making a categories folder with svg images in the scalable folder but that did not help.

Also 2nd issue is the theme contains in the places folder 3 icons: folder-download.png folder-downloads.png and folder_download.png. (All 3 were put there during design as I was having issues defining which icon name was needed and after getting it working I just left all 3 there).
Anyway the Downloads folder in home directory does not show this custom icon. All other places icons like Pictures, Videos, Music show the proper theme icon. This issue works in 17.3.

The folder-downloads issue repeats no matter what theme I use. Mint-Y, Oxygen etc.