I must say that I I don't know what could be causing this. It sounds like the tokens that we generate for the sidebar contents are somehow expiring or otherwise invalid, but I cannot reproduce that with e.g. Stand-up.
I think your best bet is to contact HipChat Support, maybe they have had similar cases and would be able to help you.
...have mention name FirstnameLastname. Fe.: @MaartenCautreels This certainly helps to know who is being mentioned in a conversation. Imagine your colleague sends the following message...
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