Correct answer is that you missed top_level_only=False (it's True by default because higher level API calls it at least twice). Then you may have 2 controls matching this criterion (maybe from different applications). find_element is a low level function. I wouldn't recommend its direct usage (the code is too long, there are many pitfalls that were taken into account on a higher level API).

>>> pywinauto.findwindows.find_element(class_name="Button", control_id=2, top_level_only=False)
Traceback (most recent call last):
  File "<interactive input>", line 1, in <module>
  File "...\pywinauto\findwindows.py", line 98, in find_element
    raise exception
ElementAmbiguousError: There are 2 elements that match the criteria {'class_name': 'Button', 'control_id': 2, 'top_level_only': False}

>>> pywinauto.findwindows.find_element(class_name="Button", title='Cancel', top_level_only=False)
<win32_element_info.HwndElementInfo - 'Cancel', Button, 395554>

Using higher level API (Application object and WindowSpecifications described in the Guide) you shouldn't care about passing process id, backend name and other things to find_element every time.

P.S. In my mind SWAPY could be significantly improved, but it's not maintained last year. I hope to re-write it in the future with smaller code base and MS UI Automation support. But currently fully automatic script generator is a higher priority.

EDIT:

This button w_open['SplitButton6'].draw_outline() could be detected as general HwndWrapper object instead of ButtonWrapper. You can check it using this:

w_open['SplitButton6'].wrapper_object()

And this is what exactly written in the Getting Started Guide (which you said you've read).

Fortunately you can use method .click_input() for any control:

w_open['SplitButton6'].click_input()

I can say more: WindowSpecification does NOT have click method. It's a method of ButtonWrapper which is instantiated dynamically. For example these statements work the same way (but Python can hide .wrapper_object() call):

w_open['SplitButton6'].wrapper_object().click_input()
w_open['SplitButton6'].click_input()

And again this is all described in the Getting Started Guide. Please read the whole guide. You will find many useful high level things. I can advise for some corner cases if something is still not clear.

Yes, Win32 applications can have existing windows that are not visible. To check visibility you can call this:

visible = app.window(title ="Trader - 23506").is_visible()

Or it might be a timing issue (if fails in ~50% cases or existing window disappears right after .exists(...) call). So another way to handle closing the dialog is:

dlg = app.window_(title ="Trader - 23506")
try:
    dlg.wait_not('visible', timeout=2)
except Exception: # or timings.TimeoutError
    dlg.close()

Instead of Application(), use Desktop() as shown below. print_control_identifiers() will print identifiers for controls and its descendants. You can use appropriate control from the output to upload your file.

from pywinauto import Desktop
app=Desktop().window(title="Open")
app.print_control_identifiers()