The section "Managed script file - create a managed/reusable script") had disappeared with all saved scripts after Jenkins upgrade to ver. 1.458.
See attached screenshot, right site 'ci:8080'
It happened after upgrading a headless system using option 'Upgrade Automatically'.

Jenkins ver. 1.458.
Managed Scripts version 0.2.0

Bug is related to the Config File Provider Plugin version 2.0.

PS Other installation (localhost on the attached screenshot) on Ubuntu system had not lost scripts and still shows all scripts and saved scripts. It has Config File Provider Plugin older version 1.2.