Getting very mixed reports of this from friends, and cannot confirm anything other than correlation, but this sounds like this could be related to having large amounts of items in the glamour dresser.

The command works fine for me on characters without items in the glamour dresser, but my main has over 700 items in theirs now, and I do remember being able to successfully use /isearch early Tuesday after the patch, as I looked for items to store in the dresser.