win32gui.EnumWindows starting with invalid window handle?

I have been using this piece of code I made for a few months now to check if a certain group of windows I have open are stuck on a certain window title for a given amount of seconds, and then closes them if so. This code is continuously ran on my VPS.

import timeimport datetimeimport win32guiimport win32processmax_downtime = 90pid_downtimes = {}cur_pids = []prev_pids = []def winEnumHandler(hwnd, ctx):    class_name = win32gui.GetClassName(hwnd)    window_text = win32gui.GetWindowText(hwnd)    if class_name != "ConsoleWindowClass":        return    if not window_text.startswith("Plutonium"):        return    if "Server restarter" in window_text:        return    if "Dedicated Server" in window_text:        return    tid, pid = win32process.GetWindowThreadProcessId(hwnd)    if pid not in pid_downtimes:        pid_downtimes[pid] = 0    pid_downtimes[pid] += 1    if pid_downtimes[pid] >= max_downtime:        print("Server restarted at:", datetime.datetime.now())        win32gui.SendMessage(hwnd, 16) # close window        return    cur_pids.append(pid)while True:    win32gui.EnumWindows(winEnumHandler, None)    old_pids = [pid for pid in prev_pids if pid not in cur_pids]    for pid in old_pids:        if pid in pid_downtimes:            del pid_downtimes[pid]    prev_pids = cur_pids    cur_pids = []    time.sleep(1)

A few days ago, for the first time it crashed.

Traceback (most recent call last):line 43, in <module>    win32gui.EnumWindows(winEnumHandler, None)line 12, in winEnumHandler    class_name = win32gui.GetClassName(hwnd)                 ^^^^^^^^^^^^^^^^^^^^^^^^^^^pywintypes.error: (1400, 'GetClassName', 'Invalid window handle.')

Anyone know what would cause this to crash after running smoothly for months? It seemed to have started the function winEnumHandler with an invalid window handle from win32gui.EnumWindows, which I didn't know was possible.