This has been a consistent on/off problem since I have regularly been using Pro in my job for the last 2 years. Say I want to "copy" a feature class into a different geodatabase with the same schema. Typically I would use "Feature Class to Feature Class" and in the Environments check "Transfer Field Domain Descriptions" in order to keep all of the domain options for my fields.
I have found that this works 50% of the time. When I open up the Fields view for the new feature class I just created using this method, the domains are not there at all. Sometimes when I exit out of Pro and re-open, they do show up. Other times they are simply lost. Sometimes the domain isn't set in the Fields view but is populated in the Domains view, so I try to set the domain on the Field and get the error "Relationship between the items already exists".
Like I said it's not consistent. Looking to see if anyone else experiences this or if there are any tips for ensuring that all the domains I need from my "original" feature class make it to my "copy" feature class in a different geodatabase. This has happened for me with both file geodatabases and enterprise SDE geodatabases.