I know that when the application is slow, there are multiple reasons like code not optimized and calling data from databases,
But the issue, I am using R shiny server pro.
The very small simple application (plotting the histogram) when loaded locally it is super fast. But when deployed on shiny server pro, it is taking time. Why is this? I understand when the code is huge and there might be delay because of this.
But this is a simple application with 10 lines of code (both UI and server) and acts slowly when deployed on shiny server pro.
Since you are not sharing any specifics about your server and network infrastructures all we can offer are guesses.
I would check for latency on the connection to the server, computational load on the server at the moment of testing, and computational power of the client computer (even if it runs on a web browser you need enough memory an CPU power to do so smoothly).