It sounds like you might have too many sessions or potentially are experience a firewall / network issue. If you contact support at https://support.atlassian.com/servicedesk/customer/portal/32 they should be able to help you diagnose the problem in more detail.
...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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