溯 (sù) literally means to travel upstream against the current; 源 means 'source.' So 溯源 = 'go upstream to the source' — a vivid image whether you mean a river, a custom, or a software bug.
usage
Often appears in the four-character set phrase 追本溯源 (zhuī běn sù yuán, 'pursue the root, trace the source') meaning 'to get to the bottom of something.'