warning: this is a rumour
The creators of SmileBASIC may be planning an in-game community feature! I'm guessing it would replace the "Web tutorial" button on the TOP MENU. This is not confirmed. Literally one person mentioned it on Twitter once.
On November 8, 2017, Miiverse will officially be shut down. Unfortunately, that means you can't upload screenshots for your programs anymore, and you can't share your programs, right?
Wrong. Enter SmileBASIC Source. It's a good resource for program keys and it even has a relatively large community! SmileBASIC programs don't rely on Miiverse to operate! smilebasicsource.com
Did you define the sprite while on DISPLAY 1? There can be two different sprites with the same ID on two different screens. (if i remember correctly) Also, 0,0 is the origin for the bottom screen, so you don't need coordinates > 240
What does your XSCREEN command look like?
If it's like XSCREEN [mode],512,[bg] then it means that you're allocating all 512 available sprites to the top screen and leaving 0 for the bottom screen. Try changing 512 to 256.