Why is growth on this Stromanthe streaked with green rather than purple undersides & some leaves have defects?

Question

This is a non-variegated Stromanthe. The new growth forming has green instead instead of purple undersides. Underside of leaves have green streaks instead of solid purple Underside of leaves have green streaks instead of solid purple Also, a few leaves have defects near base of leaf

Humidity: 54% to 60%

Temperature: 68F

Watering: when reaches 2 or 3 on the moisture meter (~7 days)

fertilizer: 0.6g 20-20-20 soluble every 4 months

pests: none detected