Feeds aren't treated as initial synced until a feed item is read, so the first item in a previously empty feed is skipped.

Found via https://github.com/matrix-org/matrix-hookshot/issues/844#issuecomment-1936584635. This is because we create a list of read guids from the items we have read, but that list is only created after we have read at least one item. See https://github.com/matrix-org/matrix-hookshot/blob/0bc49c2f2a87176c25d4be96977e076c81108376/src/feeds/FeedReader.ts#L272-L275

Probably would be fixed by #806

Start in src/feeds/FeedReader.ts at lines 272-275 and inspect how the read GUID list is created when a feed has no previously read items. Review issue #806 for the likely related work. Done means the first item in a previously empty feed is not skipped during initial synchronization.

Written by the indexing model from the issue text.