Hi Josh --
To make sure I understand what is happening, you opened a layer in Collector with a coded value domain. Then you updated the CVD through the "Fields" in the ArcGIS Online item details page for your layer, and no refreshing in Collector got the map working in Collector again (although it was working fine in ArcGIS Online).
If this is the case, it sounds like you are hitting a known bug that we are working to address (about editing a CVD while the map is open in Collector). Can you try closing Collector, then reopening it and opening the map again?
Esri Education Team