You got any fans moving air between the plants? If you're at 40% RH, then it would seem that you need more air movement. I run my fans 24/7.
One time I turned them off to do some maintenance in the room and came back over 24 hours later and turned them back on. The following day however, I discovered that I had rot setting in on one of my large colas (Yes, it can move that fast). When buds are super dense they don't get much air near the stem and it's a perfect place for spores to land and germinate. This is why it's important to have your fans running. Another benefit of the fans is that it will help beef up your stems so you don't need sticks and shit to hold up your large colas.
If you removed the affected cola and were careful not to let any of the spores float around and land on your other colas you should be fine. I had to cut the top off of a couple of my large colas and the plant did just fine without spreading rot anywhere. Just be sure fans are off, air movement is minimal, and the cola you're working on is away from other colas and plants when you do the "operation." Go in about an inch below the affected area and surgically clip the main stem and slowly remove the afflicted part of the cola and DON'T be tempted to dig into the bud while in your grow area. Take it outside of your house away from any air inlets to your grow area if you want to examine the rot.