it worked for me on the file you uploaded?
It has a Bleed and Trim Box present which are normally the reason.
Which Action List are you using or is it one you made yourself?
If you first expand the clipping mask another .25" to the right, then bleed will be generated with the default Enfocus action list. Notice on top there is already plenty of space for the mirrored image.
If you do NOT first expand the clipping mask, then the bleed on the right edge will NOT be created with the default action list.
I think the action list needs to first look and see if there is a clipping mask around the objects, then extend the mask to the edge of the bleed, then run the action to mirror the image.