I find in cases like this using my fluke 115 on min/max set to minimum voltage put into a specific point in a circuit will help you figure out if a power supply lost power when this happens. I recently acquired a fluke 376fc and it has been even more helpful with logging features in the meter that can be viewed on your smart phone in a graph showing voltages etc over whatever time frame in whatever interval you want. So you could see if a power supply looses power completely, for a split second if it just dips a little. I also have a set of double ended banana plug test leads with interchangeable types of clips to put on the end to be able to leave my meters clipped on a circuit easily. If you've never seen them fluke and knock off also make a test lead end that Is a hook that slips over a wire, then the base when twisted drives a tiny needle through the insulation so you can test almost any wire anywhere without having to be at a terminal or stripping it out.
Is this an older tac 50 (t4) or is this a tac 50-04?
I use a Fluke 289 logging meter for super intermittent issues. It’s great for proving or disproving something and you can graph the log over time and even print it out. I’ve used it for logging temperature in the machine room too.