Just to keep this visible and also for my own record, this has happened again, twice, in the last week. There is no obvious pattern to when the transactions go missing, but you can always see them disappear from the feed. This presumably means that a feed refresh is triggering the removal of items from the cached transaction list which is displayed initially.
Edit: This is currently reproducible. A transaction 1week old to within the hour is disappearing on the first feed refresh after clearing app data (I.e is visible when you start the app, but disappears after refreshing).