Errors while using VS Code extension

I try to use the VS Code extension for Isabelle 2019. When I try to open the Isabelle output I get the exception

Exception in thread "event_timer" java.util.NoSuchElementException: key not found: IsabelleDejaVuSans.ttf
at scala.collection.MapLike.default(MapLike.scala:231)
at scala.collection.MapLike.default$(MapLike.scala:230)
at scala.collection.AbstractMap.default(Map.scala:59)
at scala.collection.MapLike.apply(MapLike.scala:140)
at scala.collection.MapLike.apply$(MapLike.scala:139)
at scala.collection.AbstractMap.apply(Map.scala:59)
at isabelle.HTML$.font_face$1(html.scala:366)
at isabelle.HTML$.$anonfun$fonts_css$1(html.scala:371)
at scala.collection.immutable.List.map(List.scala:282)
at isabelle.HTML$.fonts_css(html.scala:371)
at isabelle.Present$.output_document$1(present.scala:120)
at isabelle.Present$.preview(present.scala:138)
at isabelle.vscode.Preview_Panel.$anonfun$flush$2(preview_panel.scala:33)
at scala.collection.TraversableOnce.$anonfun$foldLeft$1(TraversableOnce.scala:156)
at scala.collection.TraversableOnce.$anonfun$foldLeft$1$adapted(TraversableOnce.scala:156)
at scala.collection.Iterator.foreach(Iterator.scala:937)
at scala.collection.Iterator.foreach$(Iterator.scala:937)
at scala.collection.AbstractIterator.foreach(Iterator.scala:1425)
at scala.collection.TraversableOnce.foldLeft(TraversableOnce.scala:156)
at scala.collection.TraversableOnce.foldLeft$(TraversableOnce.scala:154)
at scala.collection.AbstractIterator.foldLeft(Iterator.scala:1425)
at scala.collection.TraversableOnce.$div$colon(TraversableOnce.scala:150)
at scala.collection.TraversableOnce.$div$colon$(TraversableOnce.scala:150)
at scala.collection.AbstractIterator.$div$colon(Iterator.scala:1425)
at isabelle.vscode.Preview_Panel.$anonfun$flush$1(preview_panel.scala:27)
at isabelle.Synchronized.change_result(synchronized.scala:73)
at isabelle.vscode.Preview_Panel.flush(preview_panel.scala:24)
at isabelle.vscode.Server.$anonfun$delay_preview$2(server.scala:210)
at isabelle.Standard_Thread$Delay.run(standard_thread.scala:64)
at isabelle.Standard_Thread$Delay.$anonfun$invoke$1(standard_thread.scala:77)
at isabelle.Event_Timer$$anon$1.run(event_timer.scala:27)
at java.base/java.util.TimerThread.mainLoop(Timer.java:556)
at java.base/java.util.TimerThread.run(Timer.java:506)

If I then do anything else (for example typing in the code window) another exception is raised every time

[Error - 9:01:48 PM] java.lang.IllegalStateException: Timer already cancelled.

How can I get rid of these two errors?

I found the same or a similar problem here, and they recommend running

$ isabelle scala
scala> import isabelle._
scala> Isabelle_Fonts.fonts(hidden = true)

Which results in

res0: List[isabelle.Isabelle_Fonts.Entry] = List(Entry("/home/daniel/opt/isabelle/contrib/isabelle_fonts-20190409/ttf-hinted/IsabelleDejaVuSans.ttf",false), Entry("/home/daniel/opt/isabelle/contrib/isabelle_fonts-20190409/ttf-hinted/IsabelleDejaVuSans-Bold.ttf",false), Entry("/home/daniel/opt/isabelle/contrib/isabelle_fonts-20190409/ttf-hinted/IsabelleDejaVuSans-Oblique.ttf",false), Entry("/home/daniel/opt/isabelle/contrib/isabelle_fonts-20190409/ttf-hinted/IsabelleDejaVuSans-BoldOblique.ttf",false), Entry("/home/daniel/opt/isabelle/contrib/isabelle_fonts-20190409/ttf-hinted/IsabelleDejaVuSansMono.ttf",false), Entry("/home/daniel/opt/isabelle/contrib/isabelle_fonts-20190409/ttf-hinted/IsabelleDejaVuSansMono-Bold.ttf",false), Entry("/home/daniel/opt/isabelle/con...