Can not add Assets to Frames

Noob user here with what I think is a simple issue, that I can not solve. I have been creating some assets, to reuse on different frames. That part works. For some reason, I am not able to consistently copy them to new frames.

I have rewatched the videos, and it looks easy. On one frame, it works, but on the others, I can not seem to get it to add. Things I have checked to try to insure I am doing this correctly include:

  • Making sure I’m in design mode, not prototype
  • I have tried moving it on the side panel. I get the black line indicator that it is under the frame, but when I release, it moves back to its original spot.
  • After I move the asset onto the frame, I tried right clicking and selecting layer, but it will not add to the one selected.

I am at a loss as to what I am doing wrong. I’m sure it is simple and stupid, so this is your chance to be a hero to a frustrated noob.