Thanks, Uwe, for looking at this. I've created my portfolio site in a kind of unusual way, using Animate CC for the slideshow of each category of images. Then I placed each .oam file published out of Animate dead center in a plain page of my Muse site. Just one .oam file on a background color with links to the other pages.
It was working with category 1, category 2, 3, 5 and then I added category 4 between 3 and 5. Suddenly, the whole site is no longer centered but is flush left. I've looked at the breakpoint properties (set to centered), tried pinning and not pinning. Now took out category 4's page. Nothing changed.
Also realized that my iPad isn't finding the tablet layout but is opening up the desktop layout and is also off to the left (and smaller on the screen in portrait than it was).
I know too little about oam files and how they behave.
Ahh....! It was because I was up late working on this. I had incorrectly chosen tablet versions for my links within the desktop layout. Threw everything off.
Sorry. But maybe it will help someone else to admit my error.