Hello Barefooted,
There are several factors that could be affecting remote monitoring, in order to be able to do live streaming you will need good internet and this happens to be the case when you are at home but not when you are out. The videos are "heavy" in the internet in special if they are HD but, if your plan for mobile data is not enough you will not be able to see them, as a starting point it is recommended to have a connection of 1Gb/1.5Gb dedicated for each one of your cameras, that means you will require about 3 gigas of internet for 2 cameras and so on, understand? At home you don't really need internet because it's a local network, if all devices are connected to the same router they can transmit data one another even when there is no internet access as long as the router can handle all that data throughput, that's why it is easier when you are at home.
The cameras can be seen locally without internet (at home) but if they are not connected to the internet they cannot be accessed from other networks, so just make sure that the cameras are connected to the internet.