This is probably the internet in the location where you’re riding. The internet speed to the house may be fine, but typically the wifi to the place where people ride is not so good.
FulGaz needs to download the ride file that contains all the elevation and distance data. It’s happened for one ride but not for the others. If you’re connected to Wifi, try it in a different part of the house, or on 4G (or vise versa). Or even try it on the wifi at a friends place or at work. They’re pretty small files, but you are the second person in the past couple of weeks who has had this problem. His solution was to use mobile data. One the ride file has been downloaded once it is saved permanently in FulGaz and doesn’t need to be downloaded again.