we have discovered a problem with very very long Private Message threads.
If you have a Private Message thread with over 500 replies, then you and the recipient will be unable to continue replying to that thread.
There is no error message and it just silently fails, which means you may think you have sent a reply but the other person will never have received your reply. You may also notice your reply is never added to the thread and is not showing up in your Sent Mail box.
The recipient may receive an email copy of the reply (if they have this enabled) but when they try to find it in their Private Messages inbox on Inkbunny, it just isn't there (and the link in the email goes to a non-existent broken private message ID).
This bug is fixed in the next site update which should be released in the next few weeks.
In the meantime the solution is to start a new Private Message thread when you reach about 500 replies.