The downloaded Facebook archive has a messages.htm file in it with my Facebook messages. But I know for sure that a lot of them are missing. My top conversation with about 65k messages has exactly 10000 messages in the messages.htm file. At the end of this conversation it says:
<div class="warning">We were unable to download the remainder of this conversation.</div>
In the past you had the ability to download an extended archive of your Facebook data but that doesn't seem to exist anymore. Is that right?
So how can I get the messages.htm file containing all my Facebook messages?