In other words: You are waiting for the empty white box to disappear
Wait for image to appear with VisualAssert does not work in this inverted case, but you can re-use the code for If {picture} then {do this}:
The loop in If {picture} then {do this} waits for the image to appear, but if you change
{
"Command": "repeatIf",
"Target": "${found} == 0",
"Value": ""
},
to
{
"Command": "repeatIf",
"Target": "${found} == 1",
"Value": ""
},
it waits for the white box image to disappear (= box content has changed).