Just seems odd to me that you'd get deficiencies so soon in any half decent compost if there wasn't some other factor involved. Was the compost made from a variety of ingredients, or was it just grass cuttings or something else specific? Organic grows shouldn't suffer from deficiencies or nute-tox in the first few weeks unless the soils is really, really bad....unless the grower is doing something else wrong. Overwatering is a prime suspect because it is very easy to love your plant to death
It probably isn't overwatering to tell the truth (that's kind of my standard IT "have you tried switching it off and on again?" response), since your leaves aren't really showing any other signs of that, but overwatering is extremely common, and causes a host of problems including pH lockouts. If it were my plant I would probably be letting the soil dry out as much as I dared after flushing and just see how it goes. It is far from terminal looking yet.