Hi Toril,
Messages are displayed on pages of up to 50. Once you fill a page, the next message will be shown on a new page. The message list display seems to open at the latest page each time.
So is it possible that the single message that you can see, is actually the first one on a new page? For example, if you previously had 50 messages, they would all appear on one page, but if you received another one, it would appear as the only message on a new page. In this case to see messages prior to this latest one, you would have to select the previous page.
If the list does have multiple pages, then you will see all available pages as a page number at the bottom left of each page ( eg. "Pages: 1 2 [3]" - with the currently displayed page within the []). If you can see a list of pages, then you need to select each page from there to see messages on it.
So look down at the bottom left of the page that you are seeing, to check if there are any other pages to select from.
Regards
Ian