Help debug screen going gray color (disconnection?)

I have a Shiny app that I'm working on and running locally. I have a reactive function that utilizes an "input" from the UI to filter some data. For some reason, in both the RStudio desktop previewer upon running as well as viewing via a web-browser, the screen goes gray when I make a change via the UI. It's the same faded gray as if it's lost the connection to the server. I've looked at the developer console in Firefox and Chrome and I don't see anything in terms of errors. I've gone into Help -> Diagnostics -> Show Log Files and nothing there seems to point to any issues. There are also no messages to the console in RStudio. Besides starting to prune down the code to a minimal working example to test, what other kinds of things can I do to help debug this issue?