Thumbnail Lag?

[Switchbox]

It can take up to 24 hours.
If you don't see any changes, try clearing your cache.

 

[MrYorkiesWorld]

I've had this happen with thumbnails, channel icons and even video titles / descriptions before. I think it must be YouTube lagging a little and taking a while to update sometimes. It can be annoying, especially when you update your banner or channel icon everywhere else, but YouTube takes about 48 hours to show it properly!

 

[Courtney Candice]

That’s happened to me a few times, just wait a little bit it should update.