Gtk-Message: GtkDialog mapped without a transient parent

I installed orca 1.3.1 on my RStudio docker (Debian GNU/Linux 9 (stretch)). I am unable to export the image and I keep getting a warning related to Fontconfig + GTK-Message that I don't know if they are related to the issue or not.

sessionInfo()
R version 3.5.3 (2019-03-11)
Platform: x86_64-pc-linux-gnu (64-bit)
Running under: Debian GNU/Linux 9 (stretch)

other attached packages:
[1] webshot_0.5.1 plotly_4.9.2.1 ggplot2_3.3.0 processx_3.4.2

I created a simple plot and when calling orca(),

> today <- Sys.Date()
> tm <- seq(0, 2, by = 1)
> x <- today - tm
> y <- rnorm(length(x))
> fig <- plot_ly(x = ~x, y = ~y, mode = 'lines', text = paste(tm, "days from today"))
> orca(fig, "foo.svg") # No error message but never finish
Unknown element "blank"tc/fonts/fonts.conf", line 100: 
Unable to revert mtime: /usr/local/share/fonts
Gtk-Message: GtkDialog mapped without a transient parent. This is discouraged.
/

What's interesting is that I tried to create another simple figure from a terminal and it did created a png file although the name of the output file is different.

root@ae51f6d6054c:/home/rstudio/doodle# orca graph '{ "data": [{"y": [1,2,1]}] }' -o foo.png
Fontconfig warning: "/etc/fonts/fonts.conf", line 100: unknown element "blank"

done with code 1 in 164.75 ms - failed or incomplete task(s)
root@ae51f6d6054c:/home/rstudio/doodle# ls foo_1.png 
foo_1.png

issue に記載されている R の orca() 呼び出しと、それに相当する orca graph CLI の呼び出しから始め、それぞれの出力ファイル名、終了ステータス、完了時の挙動を比較します。Fontconfig と GTK の警告が失敗したエクスポートとどのように関係するかを確認します。要求された画像のエクスポートが不完全なタスクを残さず正常に完了すれば完了です。