Can excessive solder paste volume contribute to components falling off the bottom of the circuit board during topside reflow?

Theoretically yes, but there are a lot of factors that would determine the point at which that would happen. The most important factor would be the ratio of solder contact surface area to component mass since the surface tension of the molten solder is what holds the parts in place during the 2nd reflow cycle.

I would not expect relatively small deviations from optimal solder volume to cause parts to fall off unless the mass of the part is too large to begin with.

You should allow for a significant factor of safety - do not expect parts to stay in place if you are close to the limit of the retention force for a given surface area. High mass, low contact area parts can be retained with thermal cure epoxy.

The epoxy would usually be applied between the solder paste screening and component placement of the 1st side process. The epoxy cures below reflow temperature, so it could be applied any time before 2nd side reflow.

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