One way that I find stray pixels.
Is to use the Fuzzy Select Tool and click somewhere within the layer,
on a "empty" space were there are no pixels.
Essentially selecting the alpha channel.
This should reveal any stray pixels,
by surrounding these pixels with a selection.

Then the Free Select Tool can be used,
to add these stray pixels to the selection and clear them.

This will work,
but when many layers are involved.
It would be advantageous to do this,
as layers are created to save time.

There is also what's know as Alpha To Selection.
Right-Click a layer within the layers dialog and the drop-down menu will open.
Select Alpha To Selection.
This will select most of what is within the alpha channel.
Some stray pixels may also be selected and also revealed.

Note: This is not to say,
that this is the only way of accomplishing this task.