Sophronitis new pb rotted at base

[Leucadian]

Thanks for the tips on hydrogen peroxide, water and heat. This is S. coccinea, that I got last spring. I bought 3 of them potted in fine bark and pumice in 2" pots, and all have done really well. I keep them moist for the most part, and they have produced 4, 4, and 3 new leads this year (they're 4n). One bloomed last year. Losing this lead knocks the plant down to 3 new growths, but that's still really good in my book. I'm just uneasy because I don't know if I caused the disease. (I just added pics of all three plants.)

I've read that S. cernua tolerates higher temps than coccinea. I have some cernuas that are mounted, but are not thriving. I think they are too dry. My growing area gets a steady ocean breeze (no salt, but cooling and drying at this time of year).