Regarding the expiration date, its not recommended to trust it after the expiration date. Even within the usable date, salt strips are questionable. IMO, it really depends on how you store and use the salt strips. Ensuring the bottle is always dry and your hands are dry when removing a strip, and finally, storing the bottle indoor and out of sunlight, will ensure a fair amount of accuracy.
Your cya level is a little on the low side and should be increased to around 75 ppm.

You can try to get a water sample directly after the cell, by loosening up the union after the cell, and after a few minutes of the cell being activated. Test the chlorine level of this water sample and compare it to the pool water. It should come out 1 to 5 ppm high than your pool water sample. This would mean its generating chlorine but being consumed quickly. Which ultimately means you have a high chlorine demand that would be satisfied by providing copious amounts of chlorine to shock levels. You may need to do this several days in a row until you can see that your chlorine residual is holding.

If you have signs of Algae starting, you may want to check your phosphate levels as well. There are phosphate treatments available, if you're high. Phosphates are algae food and helps them thrive in moderate levels of chlorine.