Got this facing Feral Chaos, have the replay to show it. Garland appeared to do his Aerial HP Assist, but he didn't - he appeared and then vanished. FC lost the Assist bar and the normal Assist summoning animation and sounds played, but no attack appeared and Garland vanished again almost immediately. Anyone else ever have this?
Come read my fanfic, Mother's Legacy. Ifalna's escape attempt fails, Aerith is raised as a SOLDIER, and the destiny of the Planet skews into the unknown. http://www.fanfiction.net/s/8143897/1/Mother-s-Legacy
Final Fantasy Wiki profile - http://finalfantasy.wikia.com/wiki/Userrake_Clawfang
It happens every once in a while.