hi there,
just a little info:
after updating my archlinux today I noticed Ardour no longer finding Calf plugins and replaced them by placeholders.
After some investigantion I found that downgrading the package “libinstpatch” to version 1.1.6-1 did the trick - whatever it means, it was a necessary quick help for me, and maybe for some others… 
suse
I ran into that situation this morning. I had just come to the theory that it was the libinstpatch upgrade that was the problem but I haven’t been able to get to that computer. Thanks for the confirmation. Now I don’t have to think about this all day at work.
I have notified the Arch packager on IRC about this issue. They believe the issue is deeper and not directly related to libinstpatch and would appreciate if you would file a bug report at https://bugs.archlinux.org/ - or connect with them via Libera.chat | #archlinux-proaudio.