Set Tile At block isn't always setting the Tile At

[UnsignedArduino]

What’s happening to you is a known bug.

I know it’s on Github somewhere…

EDIT: Here was my post encountering the same issue

Tilemaps won't update when changing tiles

WOW! That game is awesome! You have found a bug! I’ve opened an issue for it here: https://github.com/microsoft/pxt-arcade/issues/1737 Basically, the issue is that the open chest tile doesn’t appear anywhere in the tilemap. You can work around it by opening your tilemap, adding an open chest, and closing the tilemap editor. You can probably even delete the open chest from the map after is has been added at least once.

Here’s the Github issue:

You can't set a tile in a tilemap to an image that isn't in the tilemap's tileset

Although it has seemed to have been fixed in a recent version of MakeCode Arcade.