I did a drapery install a while back in a very old masonry residence, plaster over brick, real brick house, not veneer. Mortar or brick was to soft to hold to hold a Tapcon even when using a 3" one. Plastic plug for masonry also failed to hold. Finally got a hold using a long-range molly; but now that has pulled out. Maximum screw size for the bracket would be a #8. The only possible thing that I can think of it to fill the hole and whatever void exists behind it with anchoring cement, put a piece of tape over the hole to hold it, allow it to dry and try again.
If anyone has any suggestions as to a better thing to try, Post away and
TIA