This bug has been fixed!
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I have this issue as well, but only in chats with a lot of participants. I'm not sure the exact number, but my smaller chats with 11 participants or less that have all 9 icons including the paperclip, but my chats 37 participants or more, I can only see the 4 - no paperclip.
I am able to work around this where there is no paperclip by opening the file tab from the chat, then drag the file from my desktop and drop it in the files area, but it won't let me just drop it in the chat for these larger groups.