Nobody can tell you anything without exact system info or other technical details including screenshots of your comp, comp settings and so on.
Are you still facing this problem? If not, let us know how you solved it. If so, please let us know so we can assist you further.
I wasn't able to fix the problem, but my solution to get to job done quickly was to just duplicate the lights across timeline. Thus, as one turned off the next turned on. Kind of a ridiculous and tedious solution, but when you have a deadline, it doesn't matter how things are stitched together. So far I haven't seen this problem pop up again in the latest update of After Effects. If it does pop up again, I will come back with with more detail that will allow for better assist. Thank you for your patience.