Possible Reasons for Shiny App Hanging on Loading Screen

I have a shiny application that periodically (every 24 hours) interfaces with api's using croneR to run separate R scripts and save the results as csv/rds files (approximately 20, none larger than a few dozen observations).

The app works instantly locally but will not move past the 'please wait' on deployment.

I'm attempting to de-bug, are there likely causes of this that you have experienced?