Only navbar renders on iPhone

Somehow flexdashboard doen't work on iPhone properly. Only navbar renders and nothing more. It works fine on Android and my PC, but not on iPhones.

This simple example:

---
title: "Testing flexdashboard on iPhone"
output: 
  flexdashboard::flex_dashboard:
    orientation: rows
    vertical_layout: fill
    theme: bootstrap
---


```{r setup, include=FALSE}
library(flexdashboard)
library(ggplot2)
library(dplyr)
```

Row {data-height=200}
-----------------------------------------------------------------------

### Table


```{r}
DT::datatable(head(diamonds))
```

Row {data-height=350}
-----------------------------------------------------------------------

### Chart 1

```{r}
diamonds %>% ggplot(aes(cut, price, color = cut)) + geom_boxplot()
```

### Chart 2

```{r}
diamonds %>% ggplot(aes(log(price), log(carat), col = clarity)) + geom_point()
```

Results in this on iPhone:

Is there a way to fix this?
I am using flexdashboard 0.5.2, rmarkdown 2.3, R 4.0.2 and running on Windows 10 x64.
Thanks.

Start by reproducing the supplied minimal flexdashboard example on an iPhone using flexdashboard 0.5.2, rmarkdown 2.3, and R 4.0.2, then compare its rendering with Android and desktop. Trace why the navbar appears while the table and charts do not; done means the example's dashboard content renders correctly on iPhone.