crash on opening video monitor

hello,
an Ardour project I have been working on has recently developed an issue where whenever I try to open “video monitor” (which is needed for this project) the session crashes. (I have been working on the project for a few months and until recently Video Monitor has worked fine.) I am running Ardour 5.9.0 on Arch Linux 4.10.13 on a Thinkpad T420s.

here is command line and core dump output from a crash:
http://njoliat.the-nsa.org/ardour_hanemun_vid_crash_cmd.txt
http://njoliat.the-nsa.org/ardour_hanemun_vid_crash_dump.txt

and here is my ardour session file: http://njoliat.the-nsa.org/hanemun.ardour

also, around the time this issue appeared, another issue started where sometimes Ardour crashes immediately when I try to open this project.

thanks!
Nick

update: running today’s build from nightly.ardour.org seems to fix the problem.