[dmazur]

The agates are supposed to float around in their recesses. I believe it's OK for the metal cover plates to be tight.

I can't quite tell from your pictures, but if the agates aren't level, the knife edges can't rest against them correctly.

There may be some dirt under one of the agates. (? unlikely with a new scale, but stuff happens...)

You should be able to remove the metal covers, check under the agates, then reassemble everything.