someone is sharing their live location but at the moment it says “no location found“ ?

My friend is sharing her live location with me and at the moment is says “location not found”

why does this happen?

Because the Find My network can't locate the device.

Their device might be off; or it is in a location with insufficient signal; they have temporarily turned off Find My; it is in a basement carpark and lost the signal; the iPhone is in a lift which is a very effective Faraday cage; they are not in a Wi-Fi network and their phone data is off - there are many reasons.