This paper is focused on the non-linear resistance behaviours often detected by means of high resolution resistometric methods both at the very beginning of an electromigration (EM) test, and after the high stressing current inducing EM is switched off. It is shown that temperature steps, always present at the beginning or after EM, are the triggering events for different, often reversible, physical phenomena contributing to resistance changes. Precipitation-dissolution of alloyed elements is perhaps the most important one, while other mechanisms, like the combined effect of hydrostatic stress relaxation and void volume change, should cancel out. These effects, however, don't exclude a possible simultaneous effect on the resistance of accumulation/relaxation of EM damage. Experimental results are collected by means of different, complementary techniques.