A yellow 2×2 square on top. Hold it at back right: the back side shows no yellow.
Algorithms
r U2 R' U' R U' r'
7 moves
YOURS
Relations
Mirror
OLL 5
Your algorithm backwards
r U R' U R U2 r'
solves OLL 7
That's why your scrambles are never the inverse of the algorithm: you'd be practising OLL 7 without knowing it. CubeDojo builds a random state with this case and checks it comes out.