Hi Dan,
There isn't a lot of information to go on.
Perhaps if you tell us more information, we could narrowed down the problem. Let's start with the usual:
- Which platform? (Windows, Android, ...)
- What's in your Survey, are there attachments?
- Are you completely in ArcGIS Online, i.e. are the Feature Services there as well?
Have you tried capturing a diagnostic log?
1. Menu > Settings
2. Diagnostics button on the bottom
3. Choose to send the diagnostics to the log, or run AppStudio Console on the same staff WIFI to capture the diagnostics
Here's more information about using AppStudio Console
1. Go to a desktop PC which is on the same staff WIFI network
2. Download and install AppStudio for ArcGIS | ArcGIS
3. Run AppStudio for ArcGIS
4. Click Console
5. Now, go back to Survey123 and follow the steps above
6. Survey123 diagnostics should now start streaming into AppStudio Console
Stephen