I'm replying to an old post, much of it was about SD cards with the Nextion displays (for those that use email, not the web).
I got a 4.3" Nextion Enhanced display for a non-bitx project and tried HC and HC-I SD cards to get it to load the firmware. All of the attempts were made formatting the cards as VFAT32 from Linux, all were dismal failures.
What I finally had to do was format one in my wife's laptop (long format) to get it to recognize it as VFAT32. Also what I did to avoid having to format it like that again was to use dd and make an image of the blank, formatted card.
The first one I tried to use was just an HC. No go. The display still didn't like it. The second one was an HC-I card. That one worked. Also that one was formatted using the above mentioned image.
I hope this helps someone else that may encounter similar problems.
Vince - K8ZW (using the group's web interface)