I had the same experience with the gps module. The number of satellites my module can see at those situations were 1 or even 0. Check how many satellites your module can see. Also learn how many require for the accurate data from gps module. Also make sure you place your gps antenna outdoor and not in any shade or somewhere.
You know when you turn on the module, it won’t be having any data with it. I believe its the poor coverage that makes your module causing a delay to get the values after switched on. It will still transmit to the serial port, but only the valid data which it do have at that time.