Here is an example.

The missing "External face" is from a component that I deleted from the assembly.

In SW 2014, these mates automatically deleted.  Now that we are using SW 2015 (SP3) these mates no longer delete with the related component.

In this instance, I needed to remove about 20 parts from the assembly (I had overdesigned it *sheepish grin*) and am now removing the unneeded components.

The problem is, it leaves ALL the mates that referenced those components (even if ALL the components for a particular mate were deleted, the mate is still there).  I know that they look like they are suppressed, but they are not....

Now I have to go back and clean them up (I guess I don't HAVE to, but I hate a messy tree).   It is only about 10 minutes worth of work to clean them up, but it is still annoying.