It's actually not a bug : with 8.0 the nobility season has restarted. During the first 5-6 weeks, the game keeps the number of tabards you had from guild rubies of the previous season, to give you a starting boost for nobility. After a while they are removed, and now the guild only has as many tabards as your current rubies allow you to have (which is normal).
The excess tabards are removed randomly from players by the game, not by guild officiers. They need to reshuffle the reamaining ones among players again