When I build my project for Android, a white box appears over my Input Field.
Images are here:
https://imgur.com/a/v2y5hMh
I ran the project you provided from this GitHub and built it for android, and everything worked perfectly as expected.
But upon setting up my own project to work for this input method, it didn't work as expected.
I can provide further details if you need, I'm sure it's just a "check box" somewhere that I didn't press, but I've tried almost everything now.
I switched my graphics and rendering settings around.
I using Text Mesh Pro instead of the default Text component,
Used different graphics API.
Changed my camera settings, and Canvas rendering.
I am using Unity 2018.3.0f2.
If there's any other information needed to figure out this problem, I'd be happy to provide. This has been a huge problem for me for weeks.