Issue Summary

Create page editor does not start up when Jira plugin is disabled.
This bug does not affect any 10.x version, nor 9.2.x LTS.

Steps to Reproduce

1. Start the latest 9.5 instance (9.5.4)
2. Create a new page to confirm everything working as expected
3. Go to Manage Apps and disable Confluence Jira Plugin
4. Create a new page

Expected Results

Editor starts up and let's the user edit.

Actual Results

The editor doesn't finish loading.
The page title field does not render.
The status next to the Save button shows "Connecting".

Console error:

Failed to initialize plugin: customtoolbar TypeError: a.dropDown is not a function
    at b (core.js?locale=en-GB:10:266566)
    at Object.init (core.js?locale=en-GB:10:267150)
    at xP (vendors~core.js?locale=en-GB:11:570385)
    at vendors~core.js?locale=en-GB:11:571662
    at K (vendors~core.js?locale=en-GB:11:182000)
    at vendors~core.js?locale=en-GB:11:571650
    at TP (vendors~core.js?locale=en-GB:11:571701)
    at o (vendors~core.js?locale=en-GB:11:573954)

Workaround

Enable the Confluence Jira plugin