Stylesheet is getting removed/deregistered automatically

The scripts and styles were not loading on admin pages because the No-Conflict Mode setting of Gravity Forms plugin was turned ON. As the setting is designed to do so:

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As described in Gravity Forms documentation:

To temporarily resolve the issue, go to Forms > Settings and enable No
Conflict mode. This should stop third party scripts from writing to
Gravity Forms administration pages and allow you to do the things you
need.

The issue resolved after turning OFF the No-Conflict Mode.