The same thing is happening to me. I have a Note 4 and girl friend has a Galaxy 6. We have both had our phone for 6 months or so and this is the first time it has happened. It only happened on 2 texts so far. All the rest come through ok. The interesting thing is that if I copy and paste the same text and send it to her, it comes to her in the Chinese looking characters every time I send it... but other texts get to her ok.
It seems like each phone has its own emojis... and Apple definitely has different ones than those found on androids, although they have some in common. The emojis not in common with both phones are interpreted differently on the receiving phone then what the sending phone sent. The emojis are just a text code so the receiving phone must interpret it and convert it to the appropriate icon. A lot of my Apple friends send emojis that my Note 4 does not have... so my Note 4 does not know how to interpret them, therefore puts a little square in its place. But worst than that is if your phone thinks it knows what icon is associated with the text code and puts up the wrong icon. When I speak into my Galaxy Note 4 and say the words "smiley face", the sound-to-text-converter puts
into the text. When it gets to my girl friends Galaxy 6, she see a little green frog icon. Very strange.