Hello,
Same problem here. Opening that is working perfectly
in ArchiCAD 13 is buggy in version 15-16 when exported
to IFC (works in ArchiCAD). The geometry of the opening
is transferred but some of the openings is missing the hole.
The reason seems to be a changed behavior of
the WALLHOLE command. It reacts differently for the
direction of the opening -> rotating and mirroring points
the WALLHOLE out of the wall in IFC.
I succeeded to fix some bugs using WALLNICHE command,
but it is quite laborous to get things corrected.
To be honest I wish some hotfix or at least documentation
about these changes from GS.