Heya Saven,
Could be pH problem but I used the same nutes and hold pH in my water tote for weeks. You could double check the pH after everything is mixed just to double check, I would try to aim for the happy median of 6.5 pH for soil. Not sure what 1mL/L equates too ppm-wise, but I add 150ppm calmag before the rest of my micro-grow-bloom. Now in saying this, it holds pH strong for me at 5.6-5.8 which is great because I use coco. If you have the same values you might need to pH up.
Cheers and goodluck!