Have you recently changed the specs of the Adalo dropdown?
That change is causing the problem.
When the default value is empty, the place holder text is displayed.
Selecting the place holder text after selecting data from the dropdown once will unselect the selected data.
If the default value is empty, the data of the first record will be displayed.
Once the data is selected from the drop-down, it cannot be returned to the unselected data afterwards.