In LoRaWAN, any node can send a message at any time. This transmission will occur on a randomly chosen channel, with the appropriate SF.
Multiple GW can receive this message (virtually without limit). If the GW have a precise position and clock - i.e. GPS based - the backend will precisely know when each of the GW have received the message. Based on these data, the backend will be able to compute the position of the node to the precision limit.
If at the very same time another node send on the same channel and 'block' the message from the initial node to be heard from one or more gateway, it will make difficult the computation.
You need a minimum of 3 gateways to receive the same message to have some data to compute a location.
If the message is transmitted with a too low signal strength, it will limit the number of GW capable of receiving the data, preventing the location computation but still allowing the message to be received by the NW.