Two-spin resonances in double quantum dots with a constant spin-orbit coupling (SOC) can be induced by an ac field which periodically modulates the energy detuning. But a large ac field amplitude may unintentionally trigger an ac modulation in the SOC, which in turn can alter the frequency of the resonances and the form of the current peaks. Here, we demonstrate that depending on the applied magnetic field and the double quantum dot parameters a weak time dependence in the SOC can have a completely different effect on the resonant peaks; in particular, it can enhance the peaks, but it can also completely suppress them.