Emoji on MySQL and PHP: why some symbol yes other not?
Some emoji are encoded using 3 bytes. If your computers supports emoji, here are the 3 byte emoji:
☺❤✨❕❔✊✌✋☝☀☔☁⛄⚡☎➿✂⚽⚾⛳♠♥♣♦〽☕⛪⛺⛲⛵✈⛽⚠♨1⃣2⃣3⃣4⃣5⃣6⃣7⃣8⃣9⃣0⃣#⃣⬆⬇⬅➡↗↖↘↙◀▶⏪⏩♿㊙㊗✳✴♈♉♊♋♌♍♎♏♐♑♒♓⛎⭕❌©®™
The rest are encoded using 4 bytes and will not work unless you update mysql to utf8mb4. It sounds like you did not fully upgrade to utf8mb4 in some way.