Had a customer who deleted an iFrame in a Joomla article. IFrames can be trouble-some in Joomla and the old JCE, but we have JCE Pro installed. I have sometimes switched the editor from JCE to NONE in the Global Configuration. This wasn’t the fix here. When I pasted the IFrame code into the article the iframe tag would be come “<i-frame”.
I hit the X so there were no protections other than being on. Here is a link to that article. They offer more suggestions, but only this one worked for me.
I hope this helps someone else out there…