If you see a "Pending" message, the phone is not yet in Lost Mode.
Even if the phone has been powered off.......(very likely if the phone was stolen, because thieves normally do this)......it will still send out a very brief intermittent Bluetooth signal that can be picked up by another iOS device, which will forward information about the location. That is likely the location information that you are seeing at this time.
But....Lost Mode will not be implemented using this type of connection. Lost Mode will not be implemented until the phone has a good, constant, strong cellular connection and the battery is in good shape.
Another way to say the same thing.....the phone currently does not have a good strong cellular connection and/or the battery may have run down quite a bit.
Unfortunately, there is not really anything that you can do about this, except keep checking a few times each day to see if the status of the phone has changed.
Watch out for scam messages that indicate that your phone has been found and you just need to provide a bit more information so the phone can be returned to you. Apple does not get involved with lost or stolen phones, so you know that the message is not from Apple. The message is from someone who is trying to trick you into providing personal information like your Passcode and Apple account information. You need to ignore any messages like this.