Unknown trust issue in Manjaro

I have an issue similar to this issue: Cannot update Manjaro Linux: Unknown trust with Archlinux-keyring

However, my problem is that I get unknown trust even with

sudo pacman -S manjaro-keyring

I’ve tried the fixes here, but was not successful.

It may or may not be relevant, but my system crashed in the middle of downloading (but not installing) an update, which I restarted after rebooting. That’s when I noticed this problem.

Also, this answer posed that this could be a corrupt package somewhere, and would require a complete reinstall of Manjaro. How do I determine that?