I think the biggest issue with (modern, unicode) emoji has been the different art used between OS/platform. It seems like everyone is kind of converging on making their emojis convey the same emotion as Apple's (which is probably the right move since Apple popularized them, and they're baked into a ton of images that have been circulating for years)

Samsung had some rough emojis for a while. Look at their old "grimacing" face. Or the old cookies emoji that they made saltine crackers. Or their eye roll emoji which was a sarcastic eye roll on Apple, but Samsung had it as a cute smile. I'm sure that caused many a communication issue.