If your phone did get internet at some point afterwards, might have been a network glitch or just your phone needing to reboot (when something 'weird' like that happens, it helps to re-connect to the network, which I usually do by going into airplane mode and then getting out of it, instead of rebooting).
How often does this occur? It could be a sign that your phone's radios are faulty. It might be worth trying things out in a few tests to see if it is just an odd occurance or if one phone is always getting a weaker signal than the other.
Download an app like LTE Discovery on both phones. Load it up and look at the signal strength... put them side by side in a few different places, where you know there is a strong and weak signal, etc.. If one phone is always showing a weaker signal, it might have a wonky radio chip and need to be replaced.