Identify Issue: Brown Spots, Lower leaves first, from outer-tips

The location of how it is starting doesn't make sense with the symptoms shown. I'd wager something is being locked out - either pH or one of the other nutrient elements is too high in the soil. Too much p or k is possible. it's a weird one. If it is calcium it should be starting at the top, not the bottom. Were those leaves physically touching the substrate at any time? I'd be patient with this. if it stays relegated to the oldest leaves, and new growth is fine... meh. if it progresses further, it should give greater confidence in diagnosing/identifying.