Hi there, and welcome to community.rstudio.com! It's a little difficult to work with the code you've presented here. Can you please share a reprex (reproducible example)? This will ensure we're all looking at the same data and code. A guide for creating a reprex can be found here.
Without being able to run your code myself, this is a bit of a stab in the dark, but what happens if you change your eventReactive line of code to the following?:
eventReactive(input$goButton, {input$checkgroup}, ignoreNULL = FALSE)