It is constructing paths like this:

"//FileSpecifics_-1_-1.qml", "C:/.../FileSpecifics_-1_-1.qml",
"//FileSpecifics_-1_-1.qml", "//FileSpecifics_-1_-1.qml",
"//FileSpecifics.qml", "C:/.../FileSpecifics.qml", "//FileSpecifics.qml",
"//FileSpecifics.qml"

Same happens for *Pane.qml files too.

Since the paths start with //, on Windows these are interpreted as network hosts. Designer tries to connect to these and it has to wait for a timeout to continue.