I believe I've found a bug. When you set up a grid with a multiline image it shows up as a multiline text field in the web app when the appearance field starts with the width qualifier.
EG
looks like
If I remove the w2 it works as expected
looks like
Hopefully this saves someone some grief. I've wasted many hours of my life that I will never get back. haha. But that's life as a developer.
Hello @StrathconaBTS,
This is indeed a defect in the web app, I've gone ahead and logged an internal issue for this behavior. Please feel free to reach out to Esri Technical Support to log an official BUG for the issue.