File "electrum\gui\qt\network_dialog.py", line 394, in set_server
  File "electrum\network.py", line 374, in run_from_another_thread
  File "concurrent\futures\_base.py", line 435, in result
  File "concurrent\futures\_base.py", line 384, in __get_result
  File "electrum\util.py", line 1056, in wrapper
  File "electrum\network.py", line 618, in set_parameters
  File "electrum\network.py", line 637, 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 437, in assert_headers_file_available