No sprite on Flipbook - what the heck am I doing wrong?

Hey there,
I’m following a tutorial and I hit a snag. Checked a few more tutorials, and I’m coming up with the same issue. Tried some Googles. Forgive me if it’s something basic, I’m super new to Unreal.

Okay, so. I brought in some 2D sprites from and turned them into a flipbook. In the content browser, the little dude is wiggling around like he should be, but if I drag it into my scene, it’s just a blank wiggly square. And if I double click on the flipbook in the content browser, it’s just a blank wiggly square in the flipbook window too.

Is this a bug? Or am I doing something wrong?
Thanks a bunch.