It loads, actually. Problem is that there are about 50 signals, all having the informative name "learned"!! Presently, only one signal with a certain name can be contained, so there shows up only one signal.
Anyhow, it may be desirable to handle the case of non-unique names in a more graceful way. I have checked in a new version (snapshot with the same URL as before) that will rename in order to keep all signals. Also, it handles "Pages" by mapping them to CommandSets (version 4 only). Please try it.
if you drag the XCF file onto Scrutinizer Import tree list. If you click the "..." button to import a file, nothing appears to be processed.