Inventory menu script enabled on game continue

Two things:

Thing 1:

GameObject.Find() will ONLY find active GameObjects.

Thing 2:

Remember the first rule of GameObject.Find():

Do not use GameObject.Find();

More information: https://starmanta.gitbooks.io/unitytipsredux/content/first-question.html

More information: https://discussions.unity.com/t/899843/12

In general, DO NOT use Find-like or GetComponent/AddComponent-like methods unless there truly is no other way, eg, dynamic runtime discovery of arbitrary objects. These mechanisms are for extremely-advanced use ONLY.
If something is built into your scene or prefab, make a script and drag the reference(s) in. That will let you experience the highest rate of The Unity Way™ success of accessing things in your game.

“Stop playing ‘Where’s GameWaldo’ and drag it in already!”