Collapsing is a very common issue in cakes, in particular in the more traditional formulations: without stabilisers, emulsifiers, etc. In those cases opening the oven too soon, would have the steam built up in the oven and the cake release too quick, which allowed the top of the cake cool down and thus fall in or collapse. Now, with ovens that have better isolation, stabilisers in formulations it has become less of an issue.

However if you are looking at cakes in general you will see that we can have different proportions of the different ingredients, in particular in formulations were the amount of solids are not too high due to the choice of oil in stead of butter or margarine the liquid phase can become too high and will make the structure susceptible for collapsing.

Most bakers like to work with baker’s %, which is the amount of e.g. sugar compared to the amount of flour (incl starch and cocoa powder). In the case the amount of sugar gets too high (this start already at levels of 110% and higher, for the socalled high-ratio cakes). A higher level of ‘simple’ sugars, such as dextrose and fructose (in either crystalline form or via a syrup) can also influence this in a negative way.
If you are having this issue while replacing partly or fully the sugar amount by sugar replacers you might need to reconsider the type of sugar replacers you use: when going over 20% reduction in 95% of the cases that we develop sugarreduced cakes we make combinations of multiple sugar replacers, as they all have negative side-effects and by dosing them correctly the might compensate each other.