If the problem persists, you could try opening the dock (4 screws on bottom), and adding a very small amout of spacer material of some kind (like a paper shim or three) between the positioning block and the panel that it butts against. Doing so will give it a tighter fit.

This should not normally be necessary, since we hand test each dock before shipment, but the tolerance on the ethernet connector can be finicky sometimes.

Cheers