The most likely cause is a mechanical fault in the shutter/cocking linkage. On an older camera like the Aires 35V, the advance lever both cocks the shutter and resets the release mechanism. If the release parts are sticking or out of position, letting the lever snap back can trip the shutter immediately. The fact that it behaves differently at the 2-second setting also points to an internal timing/release mechanism issue rather than user error.

In short: something is likely stuck, worn, or broken inside the shutter release system. Old lubricants can also make mechanisms sluggish or unpredictable.

Since forcing it can make things worse, the practical fix is a proper service/repair (clean, lubricate, adjust) by a technician familiar with vintage leaf-shutter rangefinders. Gentle exercise may not cure it, and repeated firing could worsen wear.