There's probably something simple that I'm missing. Maybe one of the pros like @oksamurai could help us out.
From your preview it looks like there's a lot of stuff being held in the arm as triggers. I think what's happening is the "weight" of that stuff is lagging behind, causing the hand to bend on itself and feel sluggish. You might be able to fix this by either a) making the inner contents independent, or b) adding a long stick on the arm group that extends from the forearm into the props area to keep everything straight.
If it persists, please File > Export > Puppet, and upload/share your .puppet file (via Google Drive, Dropbox, Creative Cloud, etc.) here or via DM so we can take a closer look.