Labels are sometimes squashed when using TextSymbolizer with placement="line"

[mnurzia]

When rendering small road labels using a TextSymbolizer and placement="line", sometimes the spacing between characters is so small that the labels are unreadable (font used is SF Pro, but the same results were observed with DejaVu Sans Bold and other default fonts)

<TextSymbolizer 
  placement="line" 
  allow-overlap="false" 
  minimum-path-length="50" 
  repeat-distance="200" 
  face-name="SF Pro Compressed Black" 
  size="20" 
  fill="#99b3d9" 
  halo-fill="#404040" 
  halo-radius="1">
    [road_text]
</TextSymbolizer>

Even with a minimum-path-length of 50px I still get labels that are squashed. I suspected that it may have something to do with the geometry, so I tried making it easier on the renderer by I simplifying linestrings and merging them with by name. This didn't change anything. Is there an option to just disable squishing these labels? I have also tried font-feature-settings="-kern" to no avail.

Thank you for your help. Mapnik is a really awesome piece of software and other than this it's been really fun to use.