solaar 1.0.1 loses receiver occasionally

Information

Solaar version: 1.0.1 from late December 2019
Distribution: github

Describe the bug

Pairing a M310 mouse results in Solaar not showing the receiver until it has been unplugged and plugged back in. However, this happens only occasionally. The problem appears to be linked to an assertion failure in window.py.

This may be related to #444 (closed) and #493 (closed)

To Reproduce Steps to reproduce the behavior:

Start Solaar
Pair M310 mouse (new style)

Additional context

peter.patel@2030008406L:~/Samsung/github/Solaar$ bin/solaar

(solaar:5523): Gdk-CRITICAL **: 09:58:43.893:
gdk_window_thaw_toplevel_updates: assertion 'window-
> update_and_descendants_freeze_count > 0' failed
Traceback (most recent call last):
  File "/home/peter.patel/Samsung/github/Solaar/lib/solaar/ui/__init__.py", line 165, in _status_changed
    window.update(device, need_popup)
  File "/home/peter.patel/Samsung/github/Solaar/lib/solaar/ui/window.py", line 771, in update
    assert item
AssertionError
Traceback (most recent call last):
  File "/home/peter.patel/Samsung/github/Solaar/lib/solaar/ui/__init__.py", line 165, in _status_changed
    window.update(device, need_popup)
  File "/home/peter.patel/Samsung/github/Solaar/lib/solaar/ui/window.py", line 771, in update
    assert item
AssertionError
Traceback (most recent call last):
  File "/home/peter.patel/Samsung/github/Solaar/lib/solaar/ui/__init__.py", line 165, in _status_changed
    window.update(device, need_popup)
  File "/home/peter.patel/Samsung/github/Solaar/lib/solaar/ui/window.py", line 771, in update
    assert item
AssertionError
Traceback (most recent call last):
  File "/home/peter.patel/Samsung/github/Solaar/lib/solaar/ui/pair_window.py", line 75, in _check_lock_state
    if receiver.status.get(_K.ERROR):
AttributeError: 'unicode' object has no attribute 'get'
Traceback (most recent call last):
  File "/home/peter.patel/Samsung/github/Solaar/lib/solaar/ui/pair_window.py", line 120, in _finish
    receiver.status.new_device = None
AttributeError: 'unicode' object has no attribute 'new_device'