Rich text editor toggle causes rendering issues on new epics
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description
We first noticed since the Update to 17.9.2 that when creating a new epic, toggling from "plain text" to "rich text" while there is already text present in the editor-window gives an error (An error occurred while trying to render the rich text editor. Please try again.) and the Textbox appears empty in rich-text-mode. This did not to happen in another instance which is still on 17.6(.0) for testing purposes, so I assume this issue was introduced in 17.7, 17.8 or 17.9. However in the UI-Improvement-Section of those releases I did not find anything related to this specific issue, but I might have overlooked it, so I cannot pinpoint the exact release where this happens. This only happens on the new "overlayed" editor-window, e.G. when creating a new epic. Editing an existing Epic opens the editor in a bigger size, where this issue does not happen. However on new epics this happens even when using the maximize-button in the head of the editor, so this issue may not be necessarily bound exclusively to the editor window's style and size.
steps to reproduce
- gitlab-version is
gitlab-ee 17.9.2, omnibus installed on Ubuntu 22.04 - open a group with enabled epic feature
- in navigation bar: Plan/Epics
- Click on "New Epic". Overlay editor Window appears
- make sure to be in plain-text-mode. switch to it if neccessary
- enter some text into the editor's main editing-window
- switch to rich-text-mode
- editor window is now empty and error message appears between title and editor-textbox as seen in the following screenshots
rich-text-mode after switching to it:

affected gitlab-version(s)
gitlab-ee 17.9, maybe also 17.7 and 17.8, not 17.6 and earlier
System Setup
Ubuntu 22.04 x86_64 with omnibus install. Virtualized (vmware), premium plan, 5k+ users
