Overriding a core file after updating to 9.0.1

Hi! I just upgraded an 8.5 site to 9.0.1. There is a core file that I need to override:


I have placed my override file in:


… and I changed the namespace accordingly. For some reason the override does not take precedent. Concrete is still delivering the core file from updates. Before updating to 9.0.1, my override worked, but the core file was in:


Any idea what is wrong?

Thank you!

What is the namespace that you used? And did you clear the cache after making the change?