Power reception path level


I check the power reception and I have the receive signal power (RX_POWER) almost equal to the receiving signal power in the first path (FP_POWER). The value is about -80dBm.

But sometimes, the value of the receive signal power gets below -100 dBm then comes back at -80dBm in the next second while the signal power in the first path stays at about -80dBm all the time.
The antenna are not moved and nothing particular happens.
When the first path is lower than the receiving signal power then it means that the channel is not line of sight.
But what is the meaning of having a receiving signal lower than the first path ?