Can you amend your connection vars like so and retry. It might help.

conn = oracledb.connect(
    user=username, 
    password=password, 
    dsn=dsn,
    mode=oracledb.SYSDBA,
    disable_oob=True,  # Disable out-of-band breaks to maybe reduce network roundtrips
    events=True,       # Enable event notification to see if you are getting warnings
    encoding="UTF-8",  # Removes the need for char set negotiation
    nencoding="UTF-8"  # Removes the need for char set negotiation
)