Hello, I have a web map / web mapping application with 9 feature layers we host on our server and 3 ESRI feature layers. Our group has Portal for ArcGIS (local) and access to an ArcGIS Online organizational account. Currently, this web map / web mapping application sits on our Portal and we have started the process of moving it over to AGO. A few weeks ago I was able to open the Collector app, sign in to my portal account, access this web map and add new data with no trouble.
Today, I opened the Collector app (now Collector Classic) signed in with my AGO account and tried to open the web map. I received an error saying Layer Loading Timed Out. Seeing that I was able to open the Portal copy just fine, I logged out and signed in with my Portal account and received the same error. After this I downloaded the new Collector for ArcGIS app and tried these steps over again resulting in the same error message.
We have another web map with just 2 feature layers and that seems to work just fine.