GeoJson Layer not showing on browser, but working on RStudio Viewer

I have a Shiny App made with leaflet. I need to show a map, and then plot some lines from geojson files on top. This works perfectly on the RStudio Viewer, but the geojson lines are not showing on the browser.

I have checked this: it is not the browser (tried 3, and it never works), it is not the layout, not the R version, not the operative system (tried running on Windows and Linux). I tried manually adding style to the lines, and to remove the loading from the observe({...}) chunk, but it still does not work on any browser.

I have also tried to remove setView(...) and setMaxBounds(...) alternately, and the geojson lines still do not appear on the browser. The code shared here is the bare minimum used to run a basic shinyapp and test the issue. There is no additional information

I made a reprex for my app:

library(shiny)
library(dplyr)
library(leaflet)
library(jsonlite)


# Define UI for application that draws a histogram
ui <- fluidPage(

   # Application title
   titlePanel(""),

   # Sidebar with a slider input for number of bins 
   sidebarLayout(
      sidebarPanel(),

      # Show a plot of the generated distribution
      mainPanel(
        leafletOutput("map", width="100%", height="600px")
      )
   )
)


# Define server logic required to draw a histogram
server <- function(input, output) {
  gj <- readRDS("gj.rds")


  output$map <- renderLeaflet({
    leaflet() %>% addTiles() %>% 
      # Set the view
      setView(-60.704, -63.229, zoom = 13) %>%
      # Restrict the map to only show the city bounds
      setMaxBounds(-60.757, -31.556, -60.651, -31.673)
  })


  # Show the basic lines here
  observe({
    leafletProxy("map") %>% addGeoJSON(toJSON(gj), layerId = "lines")

  })
}

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

The dataset with the lines is huge, so I'm uploading a reduced version here. However, it is too big and I cant put a dput over here either. Please, download the file: https://drive.google.com/open?id=1Ib5yr2IsuGoTmOuzeyhvIe-vjXILdEnD