I've used those but the instructions aren't clear to me and I'm not always sure that it is synchronized. Hopefully it is just a software issue but it is evident that getting GPS data is not just a matter of connecting to a satellite, there is some preparation the device has to do before it is in a position to get the connection, and that can easily fail.
AGPS data just enables the Watch to get a position in a few seconds. It can get the information (almanac) from the satellites but this takes several minutes of constant direct view to clear sky. Which of the agps apps did you try? https://banglejs.com/apps/?q=agps
So far I only have used the Browser based "Assisted GPS Updater (AGPS)" one and so far have no issues.
This is great to hear. So, does that one indicate you need to sync the AGPS data from the app on the phone, and then send that down to the watch? I'm thinking it might be that I relied on the watch doing it without interacting with the phone. There are some issues in the BangleJS forums about freezing when the app is connected to the watch, so I was often not connecting the phone to the watch to avoid those freezes.