...What do you mean I may not have 0ppm CYA? You mean the testing strip is wrong or does it sometimes not show up?
You already identified the reason you're having problems. The number 1 concept taught on this site is to perform your own testing with a recommended test kit. The test strips you're using are not a test method. They are pretend testing. You probably have plenty of CYA already dissolved, but your test strips can't see it because,.........you're using test strips. If you want to solve your pool problems, it's absolutely mandatory to get one of the 2 test kits recommended by this site. Otherwise you'll be chasing this problem forever.