Hello
I have the same problem, I have tested everything as indicated and nothing changes.
My site is in development, not online.
I have a actived the excerpt with a text, but in my page Blog, the excerpt no appear, just my full text.
I use a theme child and I have test with the two codes in the function.php, nothing change.
Thank you for your help
WP 4.9.2
GP Premium 1.5.6
Elementor Free 1.9.3