Not that I have done it often, but in the handful of times I have done this, I have not had an issue with having a garment bag as a third item, but it also seems like it could depend on the day and the GA. If the GA just told the person in front of you to consolidate three items or check one, the GA will probably have to do the same to you to avoid the inevitable "how come they can have 3 items, but I can't" question and the inevitable ugly scene that follows in the wonderful times we live in. I also try to stick to mainline a/c if I have a garment bag as crews tend to be more willing to prioritize space in the closets for garment bags. I have seen FAs on OO tell pax that they will hang garment bags after boarding ends to ensure there is enough room for bags in the closet. CP did not have closets, but unfortunately that is no longer an issue.