That is the notification shown when you clear a Story Quest. In this topic, we’re talking about the issue where items move to the “Not Collected” section once you claim the reward.
Also, there’s a post in the Chit-chat topic from August 12 that mentions this issue with the qualifier “in the recent update,” so it seems to be a separate matter from the June notice.
I looked around a bit as well, but I couldn’t find any announcement about this issue on the forum.