Yes, meaning is a big problem in a physicalist framework, and I'm not aware of any satisfactory materialist account of it — which isn't surprising since I don't think one can exist. This has lead to a group of philosophers adopting "eliminative materialism," the position that all mental terms — mind, thoughts, beliefs, meanings — are "folk epistemology" and hopeless confused.

This leads to the awkward implication that eliminative materialists believe that there are no beliefs!