I will request to the production team to have a look into these items drop rate, maybe they can see something that is wrong. But as always I can't promise anything.
Please tell me a bit more detailed:
Which monster drops these items (is it an end boss drop)? and for which classes (all classe or just some)?
The more specific the details are, the easier it will be for me to direct them to the right issue.
Bone arms and shields drop from the Count Van Cliff boss at B25 Van Cliff Mansion.
Their drop rates are notoriously low and the shield only drops for hero and rare mode I believe.