I have a problem. I've got a Sharepoint List with 20 or so fields on it. 5 of them are lookups.
I've got 2 forms on my powerapp, one with 5 of those fields, one with all of them.
One of the lookups is a simple Status field. On the form with 5 fields, the dropdown values show. On the form with all of the fields, the dropdown value doesn't show. This happens on multiple lookups, HOWEVER, on 2 of those lookups the value does show.
The Sharepoint collection it is using in the "Items" property of the dropdown is a Choices collection:
Like I said this does work on one form, but not the other????
Could you please share a bit more about your issue?
Do you mean that the Dropdown box works within your form with 5 fields but not the form of all of fields?
Based on the issue that you mentioned, I have made a test on my side, and don't have the issue that you mentioned. Please consider add another Edit form (connects to your SP List) within your app, then only enable the 5 LookUp fields within this form, then try the Dropdown box again, check if the Dropdown box works well.
Please take a try to turn off the "Improved app rendering (final validation)" option within Advanced settings of App settings of your app, then re-load your app, check if the issue is fixed.
Also please take a try to re-create a new app based on your SP List, then try it again, check if the issue is fixed.