I am skipping the reprex. Will try to make the question theoretical & understandable. 
I extracted a table from server into data.frame named X.
Made Shiny app with separate ui.R and server.R files.
Plotted some graph and played with plyr functions using X.
The App run fine.
if I updated(renamed & removed variables from Global Environment) Say, Changed X to Y.
The error pops up
Error: object 'X' not found
In general, all the variable declaration is done in the server.R file.
Then why do I need to execute variable declaration commands in the console first
to make the app run, if the Global Environment is updated (Say I have renamed, removed some variables from Global Environment Not from server.R file).
Thanking You for your time and concern. 