I'm pretty sure it's not the case. Why? I just tried once again in the project that I derived from yours, and failed. Reinstalling didn't work this time.
I was trying to open a new project by myself, and failed. I got curious and noted that in all the previous projects (where I succeeded), I've installed keras there. When one installs keras, loads it and run install_keras(), which will do the following as per this documentation:
The Keras R interface uses the TensorFlow backend engine by default. To install both the core Keras library as well as the TensorFlow backend use the install_keras() function:
library(keras)
install_keras()
This will provide you with default CPU-based installations of Keras and TensorFlow.
Anyway, I noted that I succeeded to run the same code (which failed before installing keras). I don't why it's happening. Let me know whether this works for you as well or not.
And, someone please let me know the correct way to share a project. I created a new space named Other Space, changed access to Shared with initial role as Contributor and then shared the project link after changing Who can view this project to Everyone in Other Space, but enric can't access it. So, I must be missing something.