It sounds like salt build up. Feed less strong. And/or, mix enough that you get 20-30% runoff each watering. If/when it still happens, flush to get about 100% runoff. For example, if you're in a 2.5-3gal container, mix 1.5 gal of weak nutrients (1/4 to 1/2 strength) and pour all that into the soil. Go slow if you can, let it soak, then pour more. I try to give it 30 minutes to pour all that through.
Adding 1-2 Tbsp/gal of dolomite to your soil before planting may help. But, it's not going to fix overfeeding.
I have
this ppm meter for $15. When the runoff ppms get up to 1250, I know I'm heading toward a problem. 1150 is ok for me. I don't measure it much now. But, when I was struggling with salt buildup, it was very helpful to see the trend. (Now I feed half what I used to, I try to water for 20% runoff. Or, I accept that I'll have to do a larger-volume runoff in early to mid flower. I might check the runoff ppm in flower.).