Well mate I hope I'm wrong but it looks to me like it is trying to survive by cutting off the supply of nutrients to that part of the plant, my chilli plants do it. One thing is though, the reason I asked if you split it was because it is a risky things to do as it could introduce infection into the plant. You are into your 4th week of flower now and then maybe 4 weeks to go, you could be ok as the stem is quite thick and I'm sure the inside must still be ok and providing nutrients to the rest of the plant. All I can say is keep an eye on it and let us know how it goes. :)
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