what could this mean if your "elbow curve" looks like this?
First of all, you do have two elbows: one at $k=4$ and a large one at $k=8$. The second isn't very apparent because you haven't drawn out the plot for larger values of $k$. If you do you might get a figure like this:



Secondly, you aren't meant to look for an elbow when computing the silhouette score! The silhouette score accounts for both inter- and intra-cluster distance, as such it can be used for selecting $k$ on its own (i.e. select the $k$ that produces the best silhouette score).

Note: I'm not familiar with the "silhouette distance", I assume it is somewhat related to the silhouette score (maybe its inverse).

The "elbow" criterion should be used when dealing with metrics that tend to improve as $k$ increases (e.g. inertia).