I'm seeing some weird behavior (outlined below) with a Hosted View Layer. The source for the view layer is an AGOL Hosted feature layer that has attachments enabled and has three related tables as part of the service. I am the owner of the hosted feature layer, and I have AGOL admin privileges.
This behavior can be repeated. I create a view layer by clicking the Create View Layer button. I accept the default option to "Preserve Layer IDs". After the view is created, I go to the 'Settings' for the item and select the checkboxes for Enable editing, Keep track of created and updated features and Enable Sync.
If I choose to 'Add to new map with full editing control', the View - including the three related tables - is added to a new map.
If I chose to 'Add to new map', the View - including the three related tables - is added to a new map.
If I add the View to an existing map (that my account owns)
Any thoughts on what's going on, and how i can edit data in a view
The wholly unsatisfying and quite troubling answer from Esri was to republish the hosted feature layer. Esri said the source hosted feature layer had become corrupted. There was no explanation for what was corrupt about the layer or how an otherwise perfectly functioning feature layer was corrupted, but republishing solved the problem. It also caused a bunch of extra work for us as well because of republishing the layer.
In a recent AGOL update, Esri has offered up some interesting possibilities by allowing VIEWs a sort of independence from the hosted feature layer source. I haven't tried this yet, but supposedly you can update the Source for a hosted feature layer view without impacting the view.