Why does git difftool return "cannot run git-difftool--helper" error?

git difftool stopped working and I have no idea why.

# git difftool --tool=vimdiff
error: cannot run git-difftool--helper: No such file or directory
fatal: external diff died, stopping at  ...

vimdiff is installed on /bin/vimdiff and working correctly.

# vimdiff --version
VIM - Vi IMproved 7.4 (2013 Aug 10, compiled Aug  9 2019 03:17:15)

• The same problem happens when replacing the --tool to something other than vimdiff.
• It happens on any repo on that machine, so it's not a repo specific problem.
• Tried to reinstall git by yum reinstall git222-core.x86_64. The reininstall succeeded but the problem persists.
• git difftool used to work in the past on the same machine, so my guess is that something changed in the machine's configuration and causes this.
• Other git commands (status, diff, commit, push, etc) work correctly. The problem seems to be limited to git difftool.

git version is 2.22.3, running on CentOS Linux release 7.7.1908 (Core)

Any idea what could be wrong and how to further debug this?

The IUS git222 package was forked from the Fedora git package. It follows the same layout, with a minimal set of functionality in the git222-core package, and the rest of the functionality (and all their dependencies) in the main git222 package. This hasn't changed in the lifecycle of git222, so the most likely situation is that someone thought they only needed git222-core and thus uninstalled git222. To get that functionality back, install git222 again.

yum install git222