Somewhere between hour 40 save file of my save and hour 90 save file the mod "stopped working". I used it extensively to test my map but not that i'm actually starting to explore away from the core island I'm seeing nothing. I did a force scan and nothing is working and I really don't want to lose 50 hours of work. The only oddity is at one time during that save I used the Change Ore Settings mod as a "Test" but never saved the file thus I didn't think anything of it. But did this somehow break my save (e.g. did it modify the file even though I didn't hit save)?

This mod got me back into the game but pretty sure losing what I've built so far will cause me to shelve it again. Anything you can do would be greatly appreciated.

I don't have a clear answer, but there are some things to check.
So first of, this mod doesn't create the main island (that is just being done by vanilla factorio). So when you say it stopped at around 40 hours but there never are other islands this is strange to me. How did you determine it worked in the past? (before 40 hours)

I would recommend to give yourself some of the debug long range radars (either some of the legit 'Long range scanner' ones, or a few of the much faster 'long-range-scanner-debug' which you would need to cheat in) and letting them reveal the map. Please wait some minutes for them. This works better than scan commands, because the islands are created after the scan, so it may appear as water even though an island is about to be created. Also even if you use another scan command later it would take some time for the engine to actually process it.

One thing to note is that chunks are only considered as candidates when they are created for the first time. So if you for example start a save without this mod, and then add it later, there won't be any islands on water chunks that have been there already.

Adding a mod for testing, without saving shouldn't affect anything.

If you can upload it, I can take a closer look at your save. I also will need the list of mods that you are using in this save. Maybe the file factorio-current.log contains some information as well, would be good if you can provide it.

Also if you say you start exploring now, how do you do it? do you now use a boat / plane travelling outwards? (the mod is not working fast enough for this to work, thus the recommendation to explore via radars)