I noticed something interesting about Soylent recently when I looked at the list of ingredients: it contains badly absorbed forms of several vitamins and minerals.

Vitamin D2 instead of D3

magnesium oxide instead of one of the several well absorbed forms like magnesium citrate

calcium carbonate instead of calcium citrate

zinc sulfate instead of zinc picolinate, zinc gluconate, or zinc citrate

chromium chloride instead of chromium picolinate

selenium as sodium selenite instead of selenomethionine

In particular, magnesium oxide has very low bioavailability, and I would suspect that if Soylent is your only source of magnesium, you could potentially become deficient to some degree.

There are other ingredients that are not optimal, but those are perhaps less serious.