Both. Probably the splitterWe had lots of wind over the weekend and I know we lost power 2 or 3 times. I have 3 temp probes all wired directly but mine have been solid since I started using them, no anomalies. The splitter should work did both temp probes spike or just one? Looks like it was just one, if so I would just switch the probe ports and see if the spike follows the probe maybe you identify that way if it's a probe or the splitter.