Helm's plugin segfaults Ardour 6 when launched inside a virtual display

[sahabia]

HI,

Helm as a plugin makes Ardour 6 crashes with a segfault when rendering the plugin window inside a virtual display (aka VNC).

To reproduce the issue under Debian Buster, install Ardour 6.5 and Helm 0.9.0, tigervnc-standalone-server. Start VNC with tigervncserver :1 and run DISPLAY=:1 ardour6. Connect to this virtual display. Adding helm's plugin to a track leads Ardour to segfault:

[...]
Hey I'm running in Ardour!
The program 'ardour-6.5.211' received an X Window System error.
This probably reflects a bug in the program.
The error was 'GLXBadContextTag'.
(Details: serial 160 error_code 162 request_code 151 minor_code 16)
(Note to programmers: normally, X errors are reported asynchronously;
that is, you will receive the error a while after causing it.
To debug your program, run it with the --sync command line
option to change this behavior. You can then get a meaningful
backtrace from your debugger if you break on the gdk_x_error() function.)
Segmentation fault

This can't be reproduced with any other plugin. Tried: Calf-plugins, Dragonfly-reverb, Geonkick, Zyn-fusion, Surge, Ardour built-in plugins.