I am baffled by this behaviour. Everytime I install WIM_ElvUI, it gets deleted by Windows 10. None of my other addons suffer the random deletion. This is not a permissions issue, as I have WoW installed to my D:\ drive, meaning there should be no write conflicts.
As for installer clients like Twitch, Zygor, TSM, or TukUI, they don't have issues either, and WoW itself saves variables no problem. I have never seen this oddity before, and I've been scratching my head for a week or two trying to figure it out.
Just to clarify, I can unzip and install the addon, load the game, and it works; however, if I reload the UI, log out, or exit the game, then WIM_ElvUI promptly disappears. It is like Warcraft itself doesn't want that addon!