dissapearing DM member and reply ping bugs (bug or feature?)

2 strange things i bumped onto confused me, are they bugs or features?:
1. i opened DMs with another user and after an hour or so, the user was gone from my DMs, the user did not block me, this happened to me around 3 or 4 times.
2. when a reply message has ping disabled and the message gets edited, the reply will ping, this happened to me multiple times.