Overwatered
Soil pH too low
Toxic salt buildup from being in that pot too long without a flush.

Flush at water pH=6.9 (high end of the acceptable range, to raise the soil pH). You need to get those salts out of there or the stunting and burn is going to get worse FAST. Use 3x the volume of the pot and then feed with a COMPLETE fert with micros at ~1/3 the recommended dosage.

Potassium def presents as reddish speckling of the lowest leaves. Simply looking at the pH range lockout chart doesn't help until you already know what the physical symptoms presented are.