If it was maxed out at 8.2, then it could have been above. I doubt it was above 8.5 since then you'd be at equilibrium with carbon dioxide in the air vs. the water so no more would outgas. The SWG produces hydrogen gas bubbles and these outgas carbon dioxide (and a small amount of chlorine) and that causes the pH to rise.
At a pH of 8.2-8.5 and with the other numbers you had and an FC of 3.0, then that's a hypochlorous acid concentration of 0.025 which is below the minimum required for manually dosed pools which is around 0.03. Usually with an SWG pool, you can get away with a somewhat lower chlorine level, but that is only for killing free-floating algae and in your case it sounds like you've got algae stuck on walls so obviously they don't make their way to the SWG cell to get superchlorinated. At least things are now starting to make more sense. I'll bet you don't regularly (weekly or so) brush your pool. Regular brushing probably let's those with SWG pools get away with lower chlorine levels since free-floating algae would get super-chlorinated in the SWG cell.
So your pool probably has decent nutrients for algae so going below the Minimum is a problem for your pool. Though the minimum at 40 ppm CYA is 2.9 ppm FC, that's at a pH of 7.5. I would say that you should not only keep a watch on your pH, but also target a somewhat higher FC of around 4 ppm FC at your 40 ppm CYA level. That should keep the algae from growing even if the pH rose somewhat.
If you ever get a water test to find out the phosphate level of your pool, that would be good information to let us know -- not that you need to do anything about it, but since your pool is behaving near the "edge" of the minimum FC level, it would be nice to know roughly what phosphate level that is. We currently think the level where the minimum FC starts to not work is around the neighborhood of 3000 ppb so info from your pool would help validate this theory of algae growth.
Richard