1.) Check your water and soil pH. Both should be between 6 - 6.8.
If your pH is off, adjust over the course of a few days.
2.) If your pH is in range, then it looks to be a Calcium deficiency. Apply Cal-Mag & Iron solution and feed every few days or once a week.
3.) Over or under watering. Although spots don't usually occur with over or under watering, water does affect how nutrients are taken in. Too much water and the plant can't breathe to take anything in.
4.) Light burn and heat stress are always accompanied by a "taco" claw of the leaves.
What is your loght schedule?
What is your water schedule?
pH?
Nutrients?