L40 Ultra leaves a dry strip in S-shape mode

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I have set my robot to mop in an "S-shape" pattern from the app settings. However, it only performs the S-shape mopping along the edges of the room.
When it moves across the main area of the room, it just goes straight. Because of this, it leaves an unmopped, dry strip of floor right between the two mops, and it doesn't return to cover that gap.
Basically, the S-shape pattern only works on the borders, but not in the middle of the room. Could you please help me fix this issue or check if it's a software bug?

Hello,

Please select either Intensive or Deep cleaning path in the custom cleaning mode to reduce missed areas due to path selection.