TYPO3 Core

When creating a new section inside of a new inline element the eventListener is not registered for the new element.
This causes the addition of a new section to fail until the parent element is saved one time.

/typo3/sysext/backend/Resources/Public/JavaScript/FormEngineFlexForm.ts

$('.t3js-flex-container-add').on('click', function(this: HTMLElement, e: Event): void {

Changing this to

$(document).on('click', '.t3js-flex-container-add', function(this: HTMLElement, e: Event): void {

should fix this issue.

Issue also exists in Version 8 where JavaScript is used.