Flexdashboard浏览器运行报错‘Object not found’问题求助

我曾参考Stack Overflow相关内容解决过类似问题，现完整复现代码以便排查：

• 直接在R Markdown内创建数据框的Flexdashboard代码可正常运行，实现侧边栏根据selectInput选择渲染对应输出；
• 将数据框移至外部R脚本（Scripts/DataMunge.R），通过source加载的版本，本地模拟器运行正常，但在浏览器中运行时出现**‘Object not found’**错误。

本地数据框版本代码 #

---
title: "FOO"
output: flexdashboard::flex_dashboard
runtime: shiny
---

```{r global, include=FALSE}
Partner <- c("Google", "Microsoft", "Apple","Amazon")
ContactPerson <- c("Andrew","Mary","John","Barbara")
DF <- data.frame(Partner, ContactPerson)

# Create a variable called Partner Organisation
PartnerOrg <- DF$Partner

Column {.sidebar} #

selectInput(
  "Select", label = h5("Select partner organisation"), 
  choices = PartnerOrg
)
verbatimTextOutput("value")

output$value <- renderText({ 
  subset(DF, Partner %in% input$Select, "ContactPerson", drop = TRUE)
})

## 加载外部脚本版本代码
```r
---
title: "FOO"
output: flexdashboard::flex_dashboard
runtime: shiny
---

```{r global, include=FALSE}

# sys.source("Scripts/DataMunge.R", envir = knitr::knit_global())
source("Scripts/DataMunge.R", local = knitr::knit_global())

Column {.sidebar} #

selectInput(
  "Select", label = h5("Select partner organisation"), 
  choices = PartnerOrg
)
verbatimTextOutput("value")

output$value <- renderText({ 
  subset(DF, Partner %in% input$Select, "ContactPerson", drop = TRUE)
})

## 外部R脚本（Scripts/DataMunge.R）代码
```r
library(tidyverse)
library(ggthemes)
library(RColorBrewer)
library(wesanderson)
library(rsconnect)

Partner <- c("Google", "Microsoft", "Apple","Amazon")
ContactPerson <- c("Andrew","Mary","John","Barbara")
DF <- data.frame(Partner, ContactPerson)

# Create a variable called Partner Organisation
PartnerOrg <- DF$Partner

请问出现该错误的原因是什么？

内容的提问来源于stack exchange，提问作者andrew