The UE is in italics and there are no underscores around it.

That is very strange and suggest something is altering it before language parsing can take place. Do you have Translations Highlighting enabled in CB > Configuration > Integrations?

Do you have language overrides configured in CB > Plugin Management > Default language (English) for those strings? I don't have any explanation for that. I can't think of any reason for CB to do this or how it could even do this without being translated to output like that.

Ah, those are description language strings. Your Joomla editor likely just broke them with formatting. Edit the first name, last name, and username fields in CB > Field Management then fix their Description parameters so that the only thing in the field is the language string. Any surrounding HTML, etc.. will break the translation.

Usually you can click the "Toggle Editor" button so it's a plain textarea and just replace whatever is there with the raw language string then save. Joomlas editor can be pretty abusive with forcing paragraph elements around the first line, which you can also turn off in Joomlas editor settings in Extensions > Plugins > Editor - TinyMCE by setting "New Lines" to "BR Elements".