I remember the developer talking about atmosphere composition algorithm, saying that it is calculated by simulating various events and chemical reactions with other molecules of the atmosphere. Maybe also something about the presence of life and the number of active volcanoes might have effect on the result.

Historically the quantity of SO2 has always been quite high, since the earliest versions of the algorithm. This is a quote of Watsisname:

The SO2 in SE should be tweaked to only appear on planets with no oxygen creating photosynthetic life and a reducing atmosphere, as it can accumulate, but not in atmospheres with free O2.

Actually it is very hard for SO2 to accumulate even in a reducing atmosphere, as it is quickly converted to elemental sulfur via photochemical reactions.  (High energy photons will dissociate water vapor to produce free hydrogen, which then reacts with SO2.)

Do you think the code needs a fix? Can it be fixed eventually? Because we have no data to know what's the most common atmospheric composition of every type of planet, except for those who are in the solar system, but maybe if the code can be improved using recent papers we might have hope of seeing the average amount of SO2 reduced. This was also to discuss whether the amount of SO2 in SpaceEngine's planets is modeled correctly.