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Appears to be the same bug, just rendered differently on desktop. I'm on 10.12 still and saw this on some Facebook posts earlier today.
 
I have the same problem, and it seems to happen on Reddit the most, not sure why.

10.13.1 - Safari 11.0.1
 
I'm having this same problem on my new iPhone X and Messages on my Macs. Kind of a glaring bug. I hope Apple fixes it soon.
 
Are you seeing this in text that you type, or text other people have typed/sent to you?

If it's in text other people have typed, that just means the person sending it to you hasn't updated their device yet and the problem is on their end. I.e. they're sending you the odd characters and your Mac is displaying them, which is the correct behaviour.
 
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