Maybe you forgot to write a parameter to the material that is tied up to c++
First you need to define a parameter in the material node for your material. Then you need to set a Value for Texture Parameter in c++ with the same parameter name. It’s an FString name.
At the very end you need to Set Material at the end in c++ as in setting the texture on the material.
Then after that in the editor you just load the material onto the slot and it should work, the slot should display the material dynamic instance with a number.
You may want to format the texture your self in C++ because this way you get direct values in c++ on it and you tie it to the instance you have there in the same CPP page, but it may work without this part.