Hi,
I don’t know what I did exactly. I was replying a direct message while browsing some topics, and when I wanted to submit the message I had this popup:
It’s the first time I’ve seen it, and I’m puzzled with the “undefined”. I guess a more user-friendly message would be better. I don’t know if the undefined is a bug, a deleted topic or something else.
Also, which context this popup appears in exactly? 
My guess is that the original topic got deleted?
I’m puzzled. I don’t know which topic the undefined part is about, and I believe I started my message on the direct discussion page.
This is confusing. Also, I’ve written many messages on various Discourse forums and I didn’t get this popup once (which adds to the confusion), hence what I’m also asking the exact context it appears in.
As for the message itself, I’d prefer “topic not found” to “undefined”. 
I just ran into the same problem on Meta when I had the composer open in two tabs. Attempting to reply to the topic, the popup from your screenshot was displayed. That popup window is expected to be displayed, but underneath the heading, the original topic’s title should be displayed. It seems that Discourse is not finding the original topic.
When I clicked the Reply on Original Topic option, the following error was displayed:
This seems like a bug. Unless someone knows what is causing the problem, we’ll have to work out the steps to reproduce the issue. I’ll get a chance to do that today.
I can reproduce the issue on https://try.discourse.org/.
Steps to reproduce (tested with the Chrome browser on Linux):
Honestly, no idea how the ever worked, we still need a massive rewrite on composer model and controller, but at least now stuff is correctly loading and not relying on luck like it used to.
This is still happening. I don’t have steps to reproduce it, but I experienced it today.
OK, but without a repro, what exactly can we do?
Quindi ho ottenuto una riproducibilità seguendo questi passaggi:
Dovresti vedere qualcosa del genere:
Questo dovrebbe risolvere il problema:
https://review.discourse.org/t/fix-when-loading-drafts-set-the-topic/10372
Questo codice è piuttosto fragile e molto complesso da testare.
