I'm just stopping in to show my support for finding a resolution to the problem.
Very similarly, I've decided that I needed an additional field in my S123. Added it in 123Connect then republished. Everything went smoothly until I decided I also needed to add that new field to the views. As is common in AGOL, there are several possible places where a person might think this task could be handled... I tried all that I'm aware of, but was unable to add the field to the views (internal and external facing datasets). I gave up, created new views, added them to the maps, went through creating the symbology in each map, recreated all the labels in each map, and modified all html popups as I needed them. This is a lot of trouble to go through just to add a field.
I'm assuming this is a schema level issue that's likely a deeper problem that it seems on the surface. That being said, it's a problem that needs a solution if I plan to move forward using S123 as a solution for our electronic forms. Inevitably, forms will need to be edited over time so we must have a way of simply adding a field to a view without rebuilding the layer in each map every time.
Cheers.