I made changes but result is same:

    xrec = self.treedata.selection()[0]
    xrec = int(xrec[1:], 16) - 1

    print('xrec: ', xrec)
    itemXid = assetinfo_lst[xrec]
    itemXid = itemXid[1]



    Exception in Tkinter callback
    Traceback (most recent call last):
    File "C:\Users\xxxxxx\AppData\Local\Programs\Python\Python38-32\lib\tkinter\__init__.py", line 1883, in __call__
        return self.func(*args)
    File "xxxxxx.py", line 1463, in OnDoubleClick
    itemXid = assetinfo_lst[xrec]
    IndexError: list index out of range

    length of assetinfo_lst before a new insert: 16
    length of assetinfo_lst after a new insert: 17
    xrec:  xrec:  28


As I mentioned, It seems that the recent update of Windows has affected Tkinter, 
so that mainloop is not working after the first time