App icons keep disappearing

I have several apps that are stored on my SD card. Sometimes the icon for the app shows up on my homepage, sometimes all i get is a grey box that says a couple of words and a little SD card next to it. They seem to appear and disappear at random times. Anybody else having this issue and how did they fix it? thanks
Can I ask a few questions?

Is your tablet rooted?

Are you using an external SD card?

Are you using stock or a custom ROM?

When did this start to occur?