Can you check if any of the other editor buttons are also missing the insert or cancel button at the bottom? (Compare modal pop-ups between TinyMCE and JCE)
This is probably something you need to ask JCE about.
Can you give me (super) admin access so I can take a look?
You can use the 'Confidential information' button in the forum editor to hide sensitive information.
If you check all the different editor buttons when using JCE, you can see that ALL of them are missing the bottom button bar in the modal.
This includes Joomla's core editor buttons.
You should ask JCE about this. This is not an issue caused by Sourcerer.