It has happened once for me but repeatable if I reset and re-rendered.
But when I closed the render window, then opened it again, next renders rendered OK thru to end.
Has not happened again.
Some quirk but infrequent for me.
Rendering is not truly exact....every render reset render is never exactly the same....have no idea why as computers normally repeat everything exactly if user changes nothing....but apparently this program adjusts itself at times.
Doug.S