It looks like capping. A simple CLA will fix it. My Canon 7 had that issue.
Do you know if this was the last of the 12 rolls or somewhere in the middle of the batch? It does look like a capping shutter, but also check that there is no chips of film in the curtain track. Occasionally you have these small pieces stuck and they can slow down the curtain. If it was stuck on theleading edge of the 2nd curtain it could explain the "brake" effect.