Editor error: argument "msg" is missing, with no default

The following code works fine in RStudio, but throws an error in the Editor. Something related to shiny:::flushReact...

# "Add marks" button generates 'Error: argument "msg" is missing, with no default' in https://shinylive.io/r/editor/
library(shiny); library(echarty)
  ui = fluidPage(
    ecs.output("plot"),
    actionButton("add", "Add marks")
  )
  server = function(input, output, session){
    
    output$plot <- ecs.render({
      ec.init( xAxis = list(type='category',
                            data= list('Mon', 'Tue', 'Wed', 'Thu', 'Fri', 'Sat', 'Sun')),
          series.param = list( data=list(150, 230, 224, 218, 135, 147, 260), type='line' )
      )
    })
    
    observeEvent(input$add, {
      e <- ecs.proxy("plot")
      e$x$opts$series = list(
        markPoint = list(
          data = list(
            list(coord = c('Tue', 235)), 
            list(coord = c('Fri', 144))
          ),
          itemStyle = list(color='lightblue')
        )
      )
      e$x$opts$yAxis$max <- 500
      e |> ecs.exec('p_merge')
    })
  }
shinyApp(ui, server)

Reproduce the linked Shinylive R Editor example and click “Add marks” to observe the missing “msg” error. Start by tracing the reported interaction around shiny:::flushReact and the editor entry point; done means the example updates its plot without that error.