Well, haven't heard anything from SketchUp. Going through the Help Menu > Contact Us > Get Pro Technical Support - still takes you to the Google pages and a form to fill out.
But I'm - tentatively - working again.
Tracked things down to one Page of my Layout file that I was having particular trouble with. Two tables and two pieces of text containing several notes for specifications. The two tables were fine as was the one piece of text. The other piece of text was the one I was having an issue with. There was still a text element, but it was completely blank. Further, the layer that the text was supposed to be on couldn't be selected (along with another unused layer on this Page). The tables and text were all pushed to another layer. I should be thankful that they weren't stuck on a layer I couldn't select.
I started by creating a new page - all of the layers worked on the new page. So I copied and pasted the two tables and the "good" text off of the "troublesome" page onto the new page and got them on the proper layer. I had the missing text in an RTF file because it is easier to edit the text on a word processor than in Layout. So I created a new text element and pasted in the text from my RTF file. Text is fine. Move back and forth between pages. No problem. Everything is good. Delete "troublesome" page and check everything again. Still all good.
Close file. Open file back up. Text is gone - just the empty text element. Fortunately, the layers weren't screwed up this time.
So the next try was converting the RTF file to a plain TXT file in case there was some errant formatting causing problems. Tried the same steps. Created a new text element and pasted in the text from my TXT file. Text is fine. Move back and forth between pages. No problem. Everything is good.
Close file. Open file back up. Text is gone - just the empty text element.
Tried a few different variations of this. Pasted in the first paragraph. That worked. Pasted in a few paragraphs. That didn't work. Went back through the text looking for any character that might be a problem. Tried things a few more times. Finally took the text into an HTML editor because it would allow me to strip any possible code away. That finally worked. Pasted the text in, saved it, and it was still there when I reopened it.
From there I was able to reformat the text in Layout - font, tabs, underlining, etc. Saved again. Still there when I went back.
I'm still not completely out of the woods, though. One unused layer on that page is not able to be selected - I could select it when I first created this new page. Not sure when it became un-selectable. At some point in my many trials of trying to get the text to work. If you select it, it highlights but the pencil icon doesn't move to it. So you cannot put anything on that one layer on that one page. The layer is able to be selected on every other page.
Also, the Cover Page layer will not display on that one page whether it is visible or not. Curiously, it will display on every other page - except that it does not display in the proper location on any page other than the cover page. The cover page has a horizontal titleblock across the bottom of the page on this layer. Every other page has a vertical titleblock down the right side on another layer. If I turn the cover page titleblock on for any other page, it displays across the middle of the page rather than at the bottom like it does on the actual cover page.
At this point I'm just happy that I can work with my file again. The curiosities are a bit of a concern only because it shows things still aren't functioning properly. But I'll have to see if starting a new Layout file from scratch with the next project still has issues or if it is just a "legacy file" thing. I'm not going to be particularly happy if all of my Layout files from past projects have issues...
Needless to say, it has been a bit of a stressful day trying to work this out today...