[werk_ag]

SendSoilMoisture3=1 seems to not work with Wunderground, nor with Cumulus1 nor with CumulusMX, however as you noted, using SendSoilMoisture1=1 works.

Zdenek, my thought is that this behaviour is not a problem related to Cumulus (1 or MX), instead of it, the problem is how we are interpreting the use of these instructions:
SendSoilTemp1=1 (or 0)
SendSoilTemp2=1 (or 0)
SendSoilTemp3=1 (or 0)
SendSoilTemp4=1 (or 0)

When we put SendSoilTemp3=1 in Cumulus.ini, what Cumulus will do is sending to Wunderground this : "soilmoisture3=SendSoilTemp3", and currently the Wunderground webpage only shows data from "soilmoisture" which corresponds to data from Soil Sensor 1.

Resuming, the SendSoilTempX instruction in Cumulus.ini will not act as a mapping, just enables or disables sending the data of the corresponding sensor to Wunderground. Dispite Wunderground is receiving the data from soilmoisture1, soilmoisture2 and soilmoisture3, currently they don't display these data on their webpages. I'm almost sure that this is what is happening, because I wrote a simple code to try to upload directly to Wunderground from an Arduino, and only the data from sensor 1 is displayed.