This Timeout issue is not reproducible when submitting a survey with >500 image attachments on Windows, iOS, or Android devices. Success is going to depend on the size of the image attachments, the ArcGIS Enterprise timeout configuration (see https://enterprise.arcgis.com/en/server/latest/publish-services/windows/tuning-and-configuring-services.htm#GUID-2927D13A-A234-4E90-9CD2-C0515A440735) and the network upload speeds.