Pretty straightforward, the unicode character \u218e can be entered in chat, but is not rendered by the client as a box character, like \u202e is. This can likely be reproduced with other unicode characters. My steps to reproduce this:
1. Copy character to clipboard. My method was using Google Chrome's console with the command "copy('\u218e')".
2. Paste in chat
Linked issues
duplicates 1
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Comments 4
Somewhat related to MC-27138
Quote of MC-62394
Don't expect to have all 1114112 possible unicode characters integrated in Minecraft.
You're trying to enter 0x218e, not 0x218, see screenshot.