Unexplored Path sign shown on map where I've explored

[超肥的皮卡丘]

Two of them in Lower City, both next to the Scholar's Area Fast Travel.
One's at the secret room under that Fast Travel, I've solved it but an Unexplored Path sign keep showing on the map.
Leave the Fast travel room and climb up to the very top, at a corner room where you can turn left, if you see a red flag with a yellow H letter in the background, here's the second Unexplored Path sign. It seems no hidden path here.
Is this a bug or something I haven't unlocked yet?