Here's the verbose stack trace of the failing test:

======================================================================
FAIL: test_index (test.test_array.LargeArrayTest)
----------------------------------------------------------------------

Traceback (most recent call last):
  File "L:\GIT\cpython\lib\test\support\__init__.py", line 837, in wrapper
    return f(self, maxsize)
  File "L:\GIT\cpython\lib\test\test_array.py", line 1460, in test_index
    self.assertEqual(example.index(11), size+3)
AssertionError: -2147483645 != 2147483651

This looks like an overflow failure in a bigmem test (though the given limit 24Gb should accommodate that?). Do bigmem tests work on Windows?

William, you've made some sort of modifications to the versioned files, what are those?

The only modification I made was to "rt.bat" to have the value of '-u' work properly.

It's Python 3.10 on Windows built in 64-bit with Visual Studio.

Extract of test_output.log:

L:\GIT\cpython\PCbuild>"L:\GIT\cpython\PCbuild\amd64\python_d.exe" -u -Wd -E -bb -m test -u all,-curses -v -M 24Gb --header

== CPython 3.10.0a0 (heads/master-dirty:c96d00e88e, Jun 22 2020, 19:15:48) [MSC v.1926 64 bit (AMD64)]
== Windows-10-10.0.19041-SP0 little-endian
== cwd: L:\GIT\cpython\build\test_python_20756
== CPU count: 8
== encodings: locale=cp1252, FS=utf-8
(...)
test_index (test.test_array.LargeArrayTest) ...
... expected peak memory use: 4.2G
FAIL
(...)
======================================================================
FAIL: test_index (test.test_array.LargeArrayTest)
----------------------------------------------------------------------

Traceback (most recent call last):
  File "L:\GIT\cpython\lib\test\support\__init__.py", line 837, in wrapper
    return f(self, maxsize)
  File "L:\GIT\cpython\lib\test\test_array.py", line 1460, in test_index
    self.assertEqual(example.index(11), size+3)
AssertionError: -2147483645 != 2147483651

That's a bug in array_array_index() which downcasts "Py_ssize_t i" to long:

static PyObject *
array_array_index(arrayobject *self, PyObject *v)
/*[clinic end generated code: output=d48498d325602167 input=cf619898c6649d08]*/
{
    Py_ssize_t i;

    for (i = 0; i < Py_SIZE(self); i++) {
        PyObject *selfi;
        int cmp;

        selfi = getarrayitem((PyObject *)self, i);
        if (selfi == NULL)
            return NULL;
        cmp = PyObject_RichCompareBool(selfi, v, Py_EQ);
        Py_DECREF(selfi);
        if (cmp > 0) {
            return PyLong_FromLong((long)i); // <===== HERE ===
        }
        else if (cmp < 0)
            return NULL;
    }
    PyErr_SetString(PyExc_ValueError, "array.index(x): x not in array");
    return NULL;
}

New changeset 1d3dad5 by WildCard65 in branch 'master':
bpo-41085: Fix array.array.index() on 64-bit Windows (GH-21071)
1d3dad5

New changeset c6e24e7 by Miss Islington (bot) in branch '3.8':
bpo-41085: Fix array.array.index() on 64-bit Windows (GH-21071)
c6e24e7

New changeset 92f8b48 by Miss Islington (bot) in branch '3.9':
bpo-41085: Fix array.array.index() on 64-bit Windows (GH-21071)
92f8b48

Thanks William Pickard for the bug report and the fix!