Somehow I keep doing things in AE CC 2015 on a Mac and after moving keyframes or dragging the playhead around, the effects do not display. As an example, I have a couple of masks that I keyframed and were displaying, though after dragging around the current time indicator, they no longer show, even though the keyframes are still there? I cleared my cache, though that didn't fix it. Any suggestions?
Just a wild guess:
Maybe you accidentally double-clicked on a layer to open a layer panel? Then you only see this particular layer and the other parts of the comp (including their effects and masks) disappeared. You can check this by verifying that the tab of your preview panel is labeled with Composition, and not with Layer.
Now I am previewing only a single layer and the comp preview is hidden in the tab behind it.