Is this the start of rot?
It's only on the one side in this section. The base near the top of the soil doesn't show any signs of the same symptoms or rot at all, it's just on this one side edge in the lower middle section. I haven't taken it out of the soil yet to check though. The center of the really dark spots are soft, but everything else is still firm even where it's turning brown. I'm worried it's the start to rot and it'll all turn brown quick, but I'm not sure. All of the photos are of the same exact spot both front and back, not multiple different areas on the guy just for clarification!
I've had this for a little over a year and repotted it once I got it about a year ago. It's continued to grow taller and been healthy and never showed any signs of issues. He's at like 5ft+ right now and I hope I can save him or everything is ok. I have it potted in a mix of pumice, sand, calcined clay, and coconut coir. This one side has always been more pale than the rest of it even when I got it. This side was also facing the corner of the room. Last year, it was outside in the summer and then I brought it in for the winter and didn't water it much at all, if any. It was doing great inside until I just noticed these spots today along the edge today. I gave it a little water a couple weeks ago and it's still been inside since so I'm not sure if that triggered something. I really don't want to have to chop this guy at all, but if that's the only solution please give advice! Thanks!