The CYA test is the most subjective in the K-2006 and is sensitive to lighting conditions. Is it possible that one of your CYA tests was read indoors or under a cloudy sky and the other in bright sunlight?

I believe that with your FC loss, persistent (but low) CC, and your report that the walls felt slimy, you have the beginnings of trouble. I also believe that you'll do better by getting ahead of it sooner rather than later.

Follow the plan. If you feel that the actual CYA level in your pool is 35 and not 60, then use 15ppm as your minimum FC level. Other than that, follow the shock plan. Maintain FC above the minimum shock level. Keep it up until your pool passes the overnight FC loss test. Don't let the FC level drop below the minimum shock level until you're done.

The thunderstorm won't affect your pool unless you ignore the pool because of it.

Note:
I'll be around tomorrow but then I'll be pretty much offline for a couple weeks (Big Family Vacation). I'll drop a note to the rest of the PF team to look for your questions but please follow the plan, it works, it takes patience but it will work for you.

Be well.
Dave