I had this kind of issue many times with other .exe and in my experience it could most of the times be solved by :
- Moving your Oracle window from one screen to the other if you have multiple screens.
- Switching your Oracle window from "Full screen" to "Restored" or the other way.
Be carefull. If this works it will mean that your Flow won't find the field the next time if your window is not on the right screen/status.
Maybe including a step to set the window in the right position before you manipulate the form would help.
This is not a perfect answer but maybe it can help you for now until someone else explains us why it behaves like that. 😄