Can you use developer state tools and make sure the sensor exists and is that name? And if it does exist does another attribute have values like name?
It is also possible that the sensor has never been created because it is based on the other sensor. So what does this yield in developer template?
"{{ state_attr('sensor.random_pokemon','species').url }}"
It that looks correct, I would try to manyally run the HA update entity service in developer and see if it fixes it. YOU can also surf to that URL if it returns something and look at the JSON and be sure it is returning something.
UPDATE: Mine is not returning anything either now although it worked yesterday. Let me investigate, possibly they changed something
UPDATE: It looks like it does not update properly because of the template. I went to Developer ->States and selected it and forced a refresh there and it reloaded. Possibly I have to put this into templates or set the update differently.
That is the issue, it is not updating when the random_pokemon sensor changes:
This issuse I believe is a direct result of this:
My sensor.random_pokemon had two entries and only the _2 one was correct. I do not understand why this is happening in HA (what programmer though it was smart to secretly add “_2” to the “good” one, assuming you had not already used the name in something else.
I have asked a question on that group to see how to fix this as the GUI does not allow me to delete them.