Spider plants all get dried brown tips

I have 3 spider plants propagated from healthy babies. Every one of them turns out with these scraggly brown ends.

Doesn’t seem like a watering thing. I am very attentive to my plants — was probably overwatering them at some point, but for some months now, I only water my plants when the dirt is dry. I recently traveled and had a friend watering them on a strict once-a-week schedule. They are NOT being overwatered. Hard to imagine they are being under-watered though too…

In a North-facing window with comfortable (and some times high) humidity. I usually mix my out potting medium with indoor potting mix and extra perlite and bark.

Thanks!