Too much roof ventilation? It depends how you define “too much”- you might have more (or much more) roof / attic ventilation than recommended standards under one condition; it must be properly designed and balanced. (Attic Ventilation
If you install it “everywhere”, mixing all types of vents under one roof (gable, soffit, ridge, power, etc.), problems like air turbulence, and dead air pockets formation under the roof can develop. This could result in mold growth.
Besides ventilation there are of course many other “issues” that might contribute to mold growth in the attic. (Attic Mold