File "electrum\gui\qt\main_window.py", line 1613, in do_pay
  File "electrum\gui\qt\main_window.py", line 1627, in do_pay_invoice
  File "electrum\gui\qt\main_window.py", line 1664, in pay_onchain_dialog
  File "electrum\gui\qt\confirm_tx_dialog.py", line 175, in __init__
  File "electrum\gui\qt\util.py", line 336, in __init__
  File "electrum\gui\qt\confirm_tx_dialog.py", line 86, in update_tx
  File "electrum\gui\qt\main_window.py", line 1657, in <lambda>
  File "electrum\wallet.py", line 1273, in make_unsigned_transaction
  File "electrum\wallet.py", line 209, in get_locktime_for_new_transaction
  File "electrum\blockchain.py", line 490, in is_tip_stale
  File "electrum\blockchain.py", line 486, in header_at_tip
  File "electrum\blockchain.py", line 201, in func_wrapper
  File "electrum\blockchain.py", line 478, in read_header