Changing StartupImage and DisplayOffImage pics - a tip if you’re having trouble ...

I finally got around to attempting to changing the pictures on my startup image and display off image. I had the new pics of the proper format loaded on a thumb drive in folders with the correct names. I had read and viewed multiple writeups and YouTube vids about how to perform this seemingly simple task. However, after multiple attempts, I could not get the pics on the thumb drive to load. I kept getting an error message telling me the system couldn’t detect the pics (not a quote but words to that effect).
Then it hit me - I had my iPhone in my pocket and turned on while I was trying to add pics from the thumb drive. I turned off the truck, turned off my iPhone, started the truck again, and went through the procedure again. Voila!, the pics on the thumb drive loaded just fine.
Apparently, the system looks at the iPhone first and if it doesn’t find what it’s looking for, it just gives up. None of the writeups and vids I reviewed mentioned this issue.
Hope this helps others who have expressed similar problems loading new pics. Forgive me if this has been covered elsewhere on this forum. I didn’t go through all the posts on this topic but I did come across earlier posts from quite a few folks who noted they were having similar issues.