When I create a SecondaryTile with custom image, I save this image first in LocalFolder, then pass "ms-appdata:///local/.." uri to SecondaryTile constructor.
After tile is created, do I need to keep the logo image in local storage until it's unpinned? On the desktop, I create a tile, remove image from local storage, reboot PC and the tile and image are still on place. However, on the mobile, I do the same and tile ends up with no logo, just transparent.
So, does the OS keep its own cache of tile's image, or do I need to take care of it? And is this behavior any different between desktop and mobile?
I had similar problem with live tiles. Generally speaking if you want to use custom image for your tiles, you should always declare the image location, especially for the UWP that will run on the mobile devices. On the Windows 10 mobile your application is always referring to the assets folder that's why your images has disappeared.