Sharepoint O365, Visio Pro 2019.. My Visio document has about 8 pages but when I display it in Sharepoint file viewer webpart, only first page and background display. Very controlled Sharepoint environment where I have no access to the servers or administration. I feel it is some sort of setting in Visio but not sure.
Assuming you can load more documents ... can you create a simple generic Visio document with just 2 pages, one simple shape on each page, no backgrounds. See if that works. Then try 3 pages, then 4 etc ...
so Yeah. A new Visio Doc will show all pages. But if I add a new page to existing diagram it will NOT show.