An issue that has been transferred to another repository read as though it had been deleted.
GitHub follows a transfer for the issue itself but not for the things attached to it. Asking for the issue answers normally — with its new number, in its new repository — while asking for its comments answers "not found". The platform asked for both and treated the second answer as the verdict on the first, so a ticket it had just read successfully was discarded. From the outside there was no way to tell a moved ticket from a deleted one, and anything holding a reference to it could only conclude that the ticket was gone.
That was not hypothetical: an incident record pointed at a ticket that had moved, and sat in a failed state for over two weeks because every attempt to look the ticket up came back empty.
Two things changed.
A ticket that was read is now kept, even when its comments cannot be. The comment list on a ticket carries an explicit "this is the whole list" marker, so an empty list no longer means two different things — anything that actually needs the comments can tell the difference, and anything that only needs the ticket's state gets the answer it already had.
And there is now a way to ask for a ticket's state directly, without asking for its comments at all. It is one request instead of two, it follows a transfer, and it answers with the ticket's current home — so a stored reference to a moved ticket can be pointed at where the ticket now lives, instead of being abandoned and re-created.