ShinyDashboard - My third tab won't appear

Question

I am puzzled as to why I have successfully created 3 tabs in my tabBox in my R shiny app, but the third one won't appear. I would like the third tab, "Visualize", to have the checkBoxGroupInput and ggplots. Here is my code:

library(shiny)
library(shinydashboard)
library(devtools)
library(leaflet)
library(DT)
library(ggplot2)
library(dplyr)

r_colors <- rgb(t(col2rgb(colors()) / 255))
names(r_colors) <- colors()

plotdata <- read.csv("RShinyCoral.csv")
colnames(plotdata) <- c("Year1", "RLIMona", "Year2", "RLICatalina", "Year3", "RLILaParguera1998", "Year4", "RLILAPARGUERA2004")
parguera <- read.csv("RShinyCoral.csv")
parguera <- select(parguera, 5:8)
colnames(parguera) <- c("Year", "1998 Expedition", "Year", "2004 Expedition")
monaisland <- read.csv("RShinyCoral.csv")
monaisland <- select(monaisland, 1:2)
colnames(monaisland) <- c("Year", "Mona Island RLI")
islacatalina <- read.csv("RShinyCoral.csv")
islacatalina <- select(islacatalina, 3:4)
colnames(islacatalina) <- c("Year", "Isla Catalina RLI")

ui <- dashboardPage(

              dashboardHeader(
     title = "NOAA Puerto Rico Coral Luminescence (RLI, 5-year Running Average, 1730 - 1992)"
                            ), 
              dashboardSidebar(disable = TRUE),
              dashboardBody(
                              fluidRow(
                                        tabBox(
                                                 title = "", width = 12, id = "tabset1", 
                                                        tabPanel("Reef Locations", leafletOutput("mymap")),
                                                        tabPanel("Data Tables",  
                                                                   tags$a(href = "https://www.google.com/", "Click for Source Data"),
                                                                   p(), 
                                                                   fluidRow(
                                                                            column(3, 
                                                                                   actionButton("laparguera", "La Parguera Data"),
                                                                                   actionButton("mona", "Mona Island Data"),
                                                                                   actionButton("isla", "Isla Catalina Data")
                                                                                   )
                                                                           ),
                                                                   fluidRow(column(12, DT::dataTableOutput('tbl')), 
                                                                   fluidRow(column(12,  plotOutput("plot1")), 
                                                        tabPanel("Visualize", 
                                                                   fluidRow( 
                                                                            column(9, 
                                                                                   actionButton("visualize", "Add to Plot"),
                                                                   fluidRow(
                                                                     column(9, 
                                                                           checkboxGroupInput("checkbox", label = NULL, 
                                                                                            c("La Parguera",  "Mona Island", "Isla Catalina")))
            )))))))))))

server <- function(input, output) {

  observeEvent(input$laparguera, {
    output$tbl <- DT::renderDataTable(DT::datatable(parguera, options = list(pagelength = 25)))
  })
  observeEvent(input$mona, {
    output$tbl <- DT::renderDataTable(DT::datatable(monaisland, options = list(pagelength = 25)))
  })
  observeEvent(input$isla, {
    output$tbl <- DT::renderDataTable(DT::datatable(islacatalina, options = list(pagelength = 25)))
  })


  output$mymap <- renderLeaflet({
    leaflet() %>%
      addTiles() %>%
      addMarkers(lat = 17.95, lng = - 67.05, popup = "La Parguera ") %>%
      addMarkers(lat = 18.00, lng = -67.50, popup = "Mona Island") %>%
      addMarkers(lat = 18.2, lng = -69.00, popup = "Isla Catalina")
  })
  observeEvent(input$laparguera, {
    output$tbl <- DT::renderDataTable(DT::datatable(parguera, options = list(pagelength = 25)))
  })
  observeEvent(input$mona, {
    output$tbl <- DT::renderDataTable(DT::datatable(monaisland, options = list(pagelength = 25)))
  })
  observeEvent(input$isla, {
    output$tbl <- DT::renderDataTable(DT::datatable(islacatalina, options = list(pagelength = 25)))
  })

   output$plot1 <- renderPlot({
     if(length(input$visualize) == 0 ) return()
     isolate({
       if(length(input$checkbox) == 0) return()
       incheckbox <- input$checkbox
     }) # end isolate
     if(length(incheckbox) == 1) {
       switch(incheckbox,
              "Mona Island"= { gplot <- ggplot(data = plotdata) +
                geom_smooth(mapping = aes(x = Year1, y = RLIMona), fill = "navyblue", na.rm = TRUE) +
                ylab("Candelas (5-year Running Average)" ) +
                guides(fill = FALSE)
              print(gplot) },
              "Isla Catalina"= { gplot6 <- ggplot(data = plotdata) +
                geom_smooth(mapping = aes(x = Year1, y = RLICatalina), fill = "red", na.rm = TRUE) +
                ylab("Candelas (5-year Running Average)" ) +
                xlim(1837, 1992) +
                guides(fill = FALSE)
              print(gplot6) },
              "La Parguera"= { gplot7 <- ggplot(data = plotdata) +
                geom_smooth(mapping = aes(x = Year1, y = RLILAPARGUERA2004), fill = "green", na.rm = TRUE) +
                ylab("Candelas (5-year Running Average)")  +
                xlim(1853,  1992)
              print(gplot7) }
       ) # end switch
     } else if(length(incheckbox) == 2) {
       if(all(c("La Parguera", "Mona Island") %in% incheckbox)) {
         gplot2 <- ggplot(data = plotdata) +
           geom_smooth(mapping = aes(x = Year1, y = RLIMona), fill = "navyblue", na.rm = TRUE) +
           ylab("Candelas (5-year Running Average)" ) +
           xlim(1853,  1992) +
           geom_smooth(mapping = aes(x = Year1, y = RLILAPARGUERA2004), fill = "green", na.rm = TRUE) 
         print(gplot2)
       }  else if( all(c("Mona Island", "Isla Catalina") %in% incheckbox))  {
         gplot4 <- ggplot(data = plotdata) +
           geom_smooth(mapping = aes(x = Year1, y = RLIMona), fill = "navyblue", na.rm = TRUE) +
           ylab("Candelas (5-year Running Average)" ) +
           geom_smooth(mapping = aes(x = Year1, y = RLICatalina), fill = "red", na.rm = TRUE) +
           xlim(1837, 1992)
         print(gplot4)
       } else if(all(c("La Parguera", "Isla Catalina") %in% incheckbox))    {
         gplot5 <- ggplot(data = plotdata) +
           geom_smooth(mapping = aes(x = Year1, y = RLICatalina), fill = "red", na.rm = TRUE) +
           ylab("Candelas (5-year Running Average)" ) +
           geom_smooth(mapping = aes(x = Year1, y = RLILAPARGUERA2004), fill = "green", na.rm = TRUE) +
           xlim(1853, 1992)
         print(gplot5)  
       }
     }  else if ( all(c("La Parguera", "Mona Island", "Isla Catalina") %in% incheckbox)) {
       gplot3 <- ggplot(data = plotdata) +
         geom_smooth(mapping = aes(x = Year1, y = RLIMona), fill = "navyblue", na.rm = TRUE) +
         ylab("Candelas (5-year Running Average)" ) +
         geom_smooth(mapping = aes(x = Year1, y = RLILAPARGUERA2004), fill = "green", na.rm = TRUE) +
         geom_smooth(mapping = aes(x = Year1, y = RLICatalina), fill = "red", na.rm = TRUE) +
         xlim(1853, 1992)
       print(gplot3)
     } 

   })
}

# Run the application 
shinyApp(ui = ui, server = server)

And my data:

dropbox.com/s/50emrio782fosiy/RShinyCoral.csv?dl=0

Answer 1

For those who want to import madhatter5's data from dropbox, use dl=1 and readr::read_csv:

plotdata <- read_csv("https://www.dropbox.com/s/50emrio782fosiy/RShinyCoral.csv?dl=1")

And then you just need to close the parenthesis for the previous tab:

and voilá: