That is absolutely valid. This is the line that registers the afx dsl. It is spelled differently and this path is allowed in the schema.
What does the setting in path actually “Settings.Neos.Fusion.Afx” contain? The Configuration tools should show you that. Maybe the value gives a hint. You can also try to clear the caches in case some broken configuration has been cached.
Just weird guessing: I once had a case where the setting got shorter in a deployment but the cache only overwrote the parts that where new and thus some old gibberish remained at the end of the cached configuration.
Another thing i would try to exclude is that you habe PackageFactory.AtomicFusion.AFX and Neos.Fusion.Afx in your setup. The first one is deprecated and totally replaced by Neos.Fusion.Afx.
However even the older versions of this package never used this path as far as i know. So this is just a precaution for some weirdness that might happen.