I have been working on a Tablet app for the past month. It seems that a recent update has caused my drop down not to pull in the default SP value when we are using an edit form for a selected item "EditForm(OppForm)". All the other fields get populated. I'm using all OOTB fields and have not modified the PowerApps Cards for the form. I also tried removing the card then refreshing the connection then readding the dropdowncard.
For background, the name of my form is "OppForm".
Why I believe it is a bug is because when I create a new form "NewForm(OppForm)" and then back out of the form "ResetForm(OppForm)" and then when I go to edit an item "EditForm(OppForm)" it works perfectly and the drop down is populated on the edit for any item.
Knowing this workaround I created a command on my edit button to simulate what happens to see if that fixes the issue: NewForm(OppForm);ResetForm(OppForm);EditForm(OppForm). Unfortunately this did not bring my dropdown value through. This DID allows me to exit out of the edit form and when I went back into the edit form it worked.
Knowing this, I created a "Refresh" icon on the following command NewForm(OppForm);ResetForm(OppForm);EditForm(OppForm) this fixed the issue and the dropdown value displayed when the "refresh" icon was selected. The problem was that I'm also using this form for new items so I couldn't have someone click the refresh button because it would not make the form a "NewForm" any more.
I then created a work around where when I create a NewForm(OppForm) it sets a variable to 1 "VarOppForm=1". Then if someone goes into my OppForm to edit, I have the command below to run on visable If(VarOppForm=1,false,NewForm(OppForm);ResetForm(OppForm);EditForm(OppForm);VarOppForm=1).
This works, but I would like to not have crazy logic to have a basic drop down. Not sure if anyone else has encountered issues with dropdowns but it seemed to happen to me about 2 weeks ago.