Missing messages when account was unconnected to a room for some time

[chrysn]

I've observed, in two consecutive backups of a single room, that the room's first backup was incomplete; roughly a day worth of messages were missing in the middle.

The situation w/rt group members may be relevant here: I got a new account on a different server, invited my new account into the otherwise 1:1 chat, and left the old account in until I was sure to have a full backup (not trusting any server-side backups of the history -- thus matrix-archive). I used matrix-archive with the old account that's still a member of the room, but the server hasn't seen any practical activity in quite some history. Inbetween the first and the second backup, I logged in and scrolled around in the old account to verify that what matrix-backup got was indeed complete (curiously, the chat history doesn't start with "hey does this thing work?") -- appeared so, but then I ran again and noticed the diff.

I'm running this with more rooms to see whether this happens more often, and will run again on the room on which it was observed initially as well.