I didn't reply as I couldn't see where you were going wrong. You used a tried and tested recipe and appeared to use a live culture.
Ditto.
I too wondered about the evap. I always make yoghurt from fresh, unhomogenised milk, and for sure the evap will be homogenised, but I'm pretty sure lots of people make yogurt perfectly successfully from homogenised shop-bought milk using a bought yoghurt as a starter.
I have found in recent years that I get much better results buying a culture from the likes of Goat Nutrition and making my own starter culture. It seems to go on and on for generations without deteriorating, whereas using a purchased yoghurt as a starter I find it can be becoming a bit gloopy after only one or two generations. A sachet from GN costs only £3 plus postage, so is well worth the investment in my view.
linkyWhich said, of the commercial yoghurts I've used, Yeo Valley, which used to be good now has a high gloop factor after only one generation, Arla Skyr is very good and I have recultured for several generations successfully.
I don't use a yoghurt maker. I heat the raw milk on the stove top, usually to about 85C, hold that for about 10 minutes, then cool to 45C in a sink of cold water, stir in the culture (using sterilised utensils, jugs and so on) then decant into sterilised jam jars, filling all but one right to the rim, screw on the sterilised lids, and put in an insulated box along with two or three jam jars full of very hot water, with corrugated cardboard between the jars. Cover with insulation and leave until the next day. If the weather is very cold I might refresh the jars full of hot water before bedtime. The one not-completely-full jar is my test-set jar. I can see whether the mixture has set by tipping this one.
For bigger quantities, I've seen an old chest freezer with an old-fashioned 80W bulb in the lid used. The 80W bulb in the insulated space provided just the right amount of heat to keep the culture at 40-45C while the bugs do their stuff.