I recently got a Dieffenbachia plant, and now the bottom first leaves have been turning yellow and getting brown spots and splitting down the center. I've only watered when the soil was dry a few inches deep (I usually always overwater my plants so I've been very careful with this one). It sits in an East little corner nook that gets a few hours of bright sunlight. I have read that some may experience sunburn on the leaves from direct sunlight, but this spot just gets filtered bright morning/early afternoon sun, I also make sure to rotate it every week so all sides are getting sunlight. Any ideas? Help!!!

The newer leaves look okay and that is a good sign. Trim off the discolored leaves.

Water it as soon as the top one inch of soil feels almost dry. Add enough water so that a bit trickles through the drain holes.

The corner nook may be too dim. In corners, most of the plant is facing away from the light source. It prefers as much sunlight as possible without the rays of the sun falling directly on the leaves.