Kerri,
Sorry, I am just getting around to seeing this.
We have done a lot more testing since I posted this.
I am using Field Maps version 23.2.1 Build 1444 on a Google Pixel 6A running Android 13. It works fine on several different Apple iPhones and iPads even using the collector app instead of field maps.
The issue does not happen when new features are created. The full list is populated. When I edit or copy attributes the domain list is no longer populated.
It is an invasive species project and we collect both points and polygons. Both fields have different domains with a large number of options in each, but they do differ some. Neither of them populate after the initial creation of the feature and act similarly in when the work and don't work.
I have tried republishing over the existing feature layer and a totally new one, but neither work as soon as the fields are added into a form. If the fields aren't added to a form, the field populates just fine. Also if the option to use a radio buttons instead of a combo box is used. It works just fine. But that isn't practical for the number of options we have. I looked through the values that have been entered and cleaned up any that didn't match the domain, but that didn't make any difference.
I did not make or change anything on my device. It probably is a newer version of Android than previously used, but I can't make the distinction of it working and not working before and after that. This has occurred from other android users on the project as well and I don't have specifics on their devices, but they are using the newest Field Maps version that I indicated.