TL;DR: It’s probably fine to just ignore this. If you run into any issues accessing files or using your file manager after updating the grvs package and seeing these error messages, go ahead and restart your computer and it should be back to normal.
The gvfs package provides a Pacman hook that reloads the GVFS configuration after the installation, upgrade, or removal of any package that affects files in the usr/share/gvfs/ directory. It does this by signaling the gvfsd process.
gvfsd.hook · main · Arch Linux / Packaging / Packages / gvfs · GitLab
[...]
Exec = /bin/sh -c 'pkill --signal USR1 --require-handler --exact gvfsd || true'
Due to an upstream change, there is currently a bug in procps which causes pkill to incorrectly parse numeric input as base 17 instead of base 16 (that’s what causes the “not a hex string” message). Here is the relevant issue for that:
See also this issue:
Since the hook is not working correctly, it can be assumed gvfsd is not getting restarted as intended when these files are updated. As a workaround, the GRVS daemon could be manually restarted after updating the grvs package, or we can just reboot or log out/log back in.