The first time you open a LV2 plugin UI it works fine. If you then close the GUI and open it again, you get something like this:
suil error: Failed to instantiate UI <http://gareus.org/oss/lv2/avldrums#ui_gl> in /usr/lib/lv2/avldrums.lv2/avldrumsUI_gl.so
For ZynAddSubFx, it’s even worse, as you get a SIGSEGV:
#0 DGL::puglGetNativeWindow (view=0x0) at /usr/src/debug/zynaddsubfx/zynaddsubfx-3.0.6/DPF/dgl/src/pugl-upstream/src/x11.c:1287
1287 return (PuglNativeView)view->impl->win;
[Current thread is 1 (Thread 0x7f7083fbcb00 (LWP 12))]
I’m on Arch Linux, Ardour 9.2, and suil 0.10.26.
I’ve posted on suil bug tracker too: Fail to reopen LV2 plugins GUI for the second time on Ardour 9.2 (#12) · Issues · LV2 / suil · GitLab
Backtrace → https://gitlab.com/-/project/11853208/uploads/e104b7abe8abb392497d8f78772db8e5/backtrace.txt