One of the tests (test_ttk_guionly.test_variable_change) on the Ubuntu CI is intermittently hanging on this code:

    https://github.com/python/cpython/blob/e42b705188271da108de42b55d9344642170aa2b/Lib/tkinter/test/test_ttk/test_extensions.py#L147

    def test_variable_change(self):
        x = ttk.LabeledScale(self.root)
        x.pack()
        x.wait_visibility()
        ^^^^^^^^^^^^^^^^^^^

The failure at https://github.com/python/cpython/runs/697113653 gave the logs:

    0:28:29 load avg: 0.00 [425/425/1] test_ttk_guionly crashed (Exit code 1)
    Timeout (0:20:00)!
    Thread 0x00007fa268d0c080 (most recent call first):
    File "/home/runner/work/cpython/cpython/Lib/tkinter/__init__.py", line 697 in wait_visibility
    File "/home/runner/work/cpython/cpython/Lib/tkinter/test/test_ttk/test_extensions.py", line 147 in test_variable_change
    ...

The same did not happen when I re-ran the CI checks. I thought I remembered a similar issue in the past, but I couldn't find an bpo issue about it.