Can you post your dia.yml, or at least the driver snippets for the driver providing your temperature channel, and your instantiation of the transforms device?
Your driver that provides the transformed channel needs to be configured earlier in the file, prior to the transforms device instance that contains the conversion.
I'm only guessing here, but the examples as you have pasted them in also have no indentation. That may just be the forum software. If not, you'll need to unsure they are properly indented. A fuller example with indentation is attached since I can't get the forum to leave it alone. You'll need to add the driver that provides the celsius channel and 'channels' entry to refer to that channel rather than the bogus transforms.avg_temperature one.