Let me start by saying I am a self taught Photoshop dumbdumb.
I wanted to make a multi page PDF document, I found artboards and I thought this answered all of my problems. I made many boards in one doc and saved them all as PSD. When I have come back to add more only the first 'front' page is there. Have a lost all of the other pages/boards? urghhh I spent so long on it!
If parts of your document are missing that you thought were there, you might check the top of the Layers panel to see if the Layers panel content is getting filtered. To the right of the dropdown that shows "Kind," is anything selected? If so, deselect it.
If you're still having trouble, it might help if you can include a screenshot that includes your Layers panel.