I've created a Freeze-Frame in Premiere Pro, that I've tried "Replacing with an After Effects Composition" in order to animate it a bit. However, for whatever reason, the freeze-frame won't load in After Effects. I've tried this with several other images, all that worked. Far as I can tell nothing has changed from those instances to this one (aside from, obviously, the fact that I'm using a different image).
Any idea what I can do to resolve this issue?
Nobody can tell you anything without proper system info or other technical details. We know nothing about your system, your program versions, your project settings, your footage.
Temporal changes and freeze frames from Premiere Pro do not come over into AE. Neither do titles or transitions. It's a limitation you have to live with for now.