I'm on Version: 2.2.0-rc1
I have a simple drawing with the main layer and a dimensions layer
If I export as png I only see the dimensions. Both are visible in the application
If I export as pdf I get just 1 page with the leftmost side of the item and its dimension line
Page is set to landscape
I can't tell why you only see the dimensions with export to png. But export to bitmap is unreliable anyway. Better export to pdf and convert to bitmap in a different application if you really need it.
There have been issues with paper orientation reverting from landscape to portrait or vice versa, I don't remember the details, with letter or other US paper sizes. So this could be the reason for only the leftmost side shown. This bug has been solved in more recent versions.
Also export to pdf from within the Print Preview mode to be sure to get the wanted scale and position on the paper or pdf format.
You might provide a sample file here to inspect if you can't solve it.