Let me be more specific. The composition (and energy level) determines whether the nucleus is stable or not. In that sense, the stability or instability is cased. If it is unstable, the timing of the decay is completely probabilistic. There is no difference between a nucleus that is about to decay and one that is not. In that sense, there is no cause to the decay.
Yes but can it be "influenced" Or isn't it known that there is an influence? I consider it beyond the scope of determination for several factors. But we have discovered several mechanisms as contributing factors.