File "electrum\gui\qt\network_dialog.py", line 411, in set_server
  File "electrum\network.py", line 392, in run_from_another_thread
  File "concurrent\futures\_base.py", line 439, in result
  File "concurrent\futures\_base.py", line 388, in __get_result
  File "electrum\util.py", line 1091, in wrapper
  File "electrum\network.py", line 639, in set_parameters
  File "electrum\network.py", line 659, in switch_lagging_interface
  File "electrum\blockchain.py", line 486, in header_at_tip
  File "electrum\blockchain.py", line 201, in func_wrapper
  File "electrum\blockchain.py", line 473, in read_header
  File "electrum\blockchain.py", line 435, in assert_headers_file_available