A bit of a follow-up - I just found that running with LIBGL_ALWAYS_INDIRECT=true gets rid of the black triangle problem.
- Bug#1004007: freecad: Segfaults on armhf when clicking &qu... Serge Schneider
- Bug#1004007: freecad: Segfaults on armhf when clickin... Tobias Frost
- Bug#1004007: freecad: Segfaults on armhf when clickin... serge
- Bug#1004007: freecad: Segfaults on armhf when clickin... serge