If you can’t downgrade pango lib one user has the following workaround:
One thing I did find by googling was this issue that seemed related: https://bugs.archlinux.org/task/48827
It mentions libfontconfig, so I tried renaming the libfontconfig.so bundled with Insync and then symlinking the system one (from the fontconfig-infinality-ultimate 2.11.95-3 package from https://wiki.archlinux.org/index.php/Infinality). That seemed to have fixed the issue for now.