Greek letters in R expressions result in missing glyph - r

Question

When I use Greek letters in a plot label in R on Fedora 31, the expression will not be properly rendered. Instead of the Greek letter, a missing glyph box appears in the label. The same code works properly on rstudio.cloud. The same behavior can also be observed in ggplot. See the reprex below for an example.
As I understand it, R takes an OS default font for text in plots. This seems to be Liberation Sans in my case. I do not get the problem here, as Liberation has glyphs for the Greek alphabet.
Any help would be appreciated.
Edit
Further investigation resulted in some weird things. I ran the code from terminal and the same thing happens. But within RStudio, when I execute x11() before running plot, then the output is rendered properly in the x11 window.
The strange thing about this is, that x11 appears to be the default graphics device when running the code from the terminal. However, even if I run x11() beforehand in the terminal, it returns a plot with the missing glyph box.
After learning that this has something to do with the graphics device, I tried various graphics devices with ggsave(). With all the formats I tried, the expression was rendered properly.
What is not yet clear to me is the source of the problem. Is this a bug in the R binary from dnf? Or where could the issue lie? I do remember that it work with Fedora 30 a couple of months ago.
plot(Sepal.Length ~ Sepal.Width,
iris,
xlab = expression(beta))
Created on 2020-03-06 by the reprex package (v0.3.0)
devtools::session_info()
#> ─ Session info ───────────────────────────────────────────────────────────────
#> setting value
#> version R version 3.6.2 (2019-12-12)
#> os Fedora 31 (Workstation Edition)
#> system x86_64, linux-gnu
#> ui X11
#> language (EN)
#> collate en_US.UTF-8
#> ctype en_US.UTF-8
#> tz Europe/Berlin
#> date 2020-03-06
#>
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