There are reports of a crash of GDL here and here (scroll down to the bottom of page) with recent versions og PLPLOT and WXWIDGETS.
My tests show that the reported error comes, at least, when the plplot library (the wxWidgets part, obviously) has been compiled with a version of wxWidgets older than 3.1.5
When plplot is compiled with the wxwidgets 3.1.5 installed, the error and crash is not present.
Unfortunately, the distributed version ofplplot[-wxwidgets] for suse tumbleweed and Kubuntu 20.04
exhibit the problem (for which I've no clue).
according to this report it disappears when plplot is 'recompiled' after wxwidgets. Please report this problem to suse, ubuntu... packagers.