R Shiny JS jump to last page conflicting with auto generate value in new row

I have a Shiny app that allows the user to enter their project details to the database. This is achieved by the Add Project Details Button that adds an empty row to the table. When the add button is clicked the app auto generates the next reference number (under column Reference.Number) in the new row based on the previous one.

Another function of the Add button is also to make the app jump to the last page of the table rather than having the user click on the last page number under the table.

The app almost works fine because when I click the Add button, the app does temporarily go the last page, but as soon as the auto generate value is calculated, the app goes back to the first page of the table.

What could be causing this conflict and how can this be fixed?

Sample data (df):

df <- structure(list(Reference.Number = c("33331", "33332", "33333", 
                                          "33334", "33335"), 
                     Request.Date = c("1/6/2022", "1/6/2022", "1/19/2022", 
                                                                              "1/20/2021", "1/24/2022"), 
                     Requestor.Name = c("Comm Dist 3 by Kitty", "Comm Dist 3 by Kitty", "Updated maps for David", "    Stone Cold", "Updated SOE 60 inch wall map"),
                     Requestor.Dept.Div = c("C 3 Staff",    "C 3 Staff", "Unincorp & Comm", "Mt.Rushmore AME Church Ft. Billy",                                         "SOE"), 
                     Requestor.Phone = c("", "", "", "", ""), 
                     Contact.Person = c("Tommy",                             "Tommy", "Bob", "Bob", "Joe"),
                     Contact.Phone = c("1111",                               "2222", "3333", "ext 1111", "3434"),
                     Deadline = c("1/20/2022",         "1/20/2022", "1/22/2022", "", "1/24/2022"),
                     Project.Description = c("45x36 portrait map ",          "45x36 portrait map  ",   "24x24 Unincorporated areas", "Percent Females Aged 25 - 55  Below Poverty Level By Zip Code",                "SOE Wall Map 60x60 p"), 
                     Project.File.Location = c("", 
                                                  "", "C:\\ABC\\Tommy\\work|Map-Projects\\BD Unincororated\\#14785 Unincorporated 24x24.pdf", 
                                                  "C:\\ABC\\Demographics\\Demographic_Request\\FemalesAge10-18BelowPoveryLevel\\FemalesAge10-18BelowPoveryLevel.aprx", 
                                                  "C:\\ABC\\Tommy\\work|Map-Projects\\BD Unincororated\\#14786 V P 60x60.pdf" 

Code:

library(shiny)
library(shinythemes)
library(DT)
library(tidyverse)

# Define UI for application 
ui =   navbarPage(tags$style("table, .table {color: unset;} .dataTable th, .datatables input {color: white}"),
                  title = div("GIS Team Projects"),
                  theme = shinytheme("cyborg"),
                  tabPanel("GIS Projects",
                           icon = icon("info"),
                           div(p(h1("Instructions:"),style="text-align: justify;")),
                           p("1. The user can add their project details.", style="color:black"),
                           uiOutput("all"),
                  sidebarLayout(
                    sidebarPanel(
                      actionButton("addData", "Add Project Details"),
                      ),
                    mainPanel(
                      downloadButton("download1","Download data as csv"),                
                      DTOutput("contents"),
                      tags$script(HTML("
           Shiny.addCustomMessageHandler('messageJumpToLast', function(message) {
               // select the target table via its container ID and class:
               var target = $('#contents .dataTable');
               // display last page:
               target.dataTable().api().page('last').draw(false);
           });
           "))),
                    )
                    )
)

# Define server logic required 
server <- function(input, output) {
  
  myData = reactiveVal(df)
  
  # Create an 'empty' tibble 
  user_table =  
    df %>% 
    slice(1) 
  
  user_table[1,]<-NA
  
  # Display data as is
  output$contents =
    renderDT(myData(),
             server = FALSE,
             editable = TRUE,
             options = list(lengthChange = TRUE),
             rownames = FALSE)
  
  # Store a proxy of contents 
  proxy = dataTableProxy(outputId = "contents")
  
  # Each time addData is pressed, add user_table to proxy
  observeEvent(eventExpr = input$addData, {
    myData(myData() %>% bind_rows(user_table %>% 
  mutate(Reference.Number=as.character(max(as.numeric(myData()$Reference.Number), na.rm = T)+1))))
  session$sendCustomMessage('messageJumpToLast', 'some payload here, if needed') # Don't know if this should be added or not!
  })
  
}

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