I can think of a number of things.
The most obvious is to make sure the bones have a strength value greater than 0. When the
Strength of a bone is set to 0, it won't move anything using
Flexi-binding. (Note:
Bind Layer and
Bind Points don't require bone strength.)
If Bone Strength looks okay, check that you aren't using Bind Layer in a parent group. The Bind Layer tool is for rigidly binding a layer to a single bone, and when this layer is a group, that includes its child layers.
If that isn't it, the layers have probably been released from binding, so nothing affects them. At this point, it's easier to just reset the layer binding. Select the layers in question and choose
Reset All Bone Rigging command. This command resets only the
selected layers. (Note: if you don't select any layers, Moho will assume you wish to reset ALL layers, so be careful.)
What 'reset' means is that the layers get the
default Flexi-binding setting, so all bones will affect the selected layers.
If you want to limit Flexi-binding of the layers to
specific bones, you can select all the layers you wish to bind, the bones you wish to bind them to, and choose
Use Selected Bones for Flexi-binding. This will bind the entire selection of layers to the selected bones in one go. Very convenient!
Note: the above steps work for Moho 14 as well, but Use Selected Bones For Flexi-binding has been renamed
Link Bones, and instead of selecting a menu command, you can simply click the Link Bones button
, which is even more convenient! 
