🇮🇳India @mahtoranjeet

I could not able to reproduce this on fresh installation
I have installed a fresh drupal 8.
I have 'node/2' aliased as 'home'
In Site Config page I set the homepage as 'node/2'.
then I print $variables in preprocess function. it print
[is_front] => 1
After that
In Site Config page I set homepage as 'home' and save it.
Then I print $variables it print
[is_front] => 1

Either you set homepage as node/nid (node/2) or its aliased (home) it returns true.