If temps, humidity and lighting is all good then the question is...

Do you have nutrients in your soil? ABG mix and stuff like that is typically very dead that's the intention after all. No nutrients=no mold. But plants need it too so you need to add something to make sure your plants get feed too.

The nitrogen cycle is the key to plant growth. Simplified its like this. Waste>eaten by isopods/springtails/bacteria>becomes nitrogen that the plant use to grow and make fruit etc>eaten by large animals>becomes waste and the cycle goes around like that.

But in a viveriums we give our animals food from another source since our enclosure ecosystem is not large enough to take care of the entire cycle.

So your goal here is to naturally generate nitrogen so your plants can thrive. Outside of a viveriums we give fertiliser to plants to make sure they have what they need. But synthetic fertilisers are often poisonous to the animals we keep in viveriums.

There one thing that you can use, aquatic fertiliser. Stuff used in aquariums. But it should never be the solution it should just be a crutch until you have an isopod population that can maintain the habitat by you feeding them. And if you have pots in the wall etc don't forget to attract isopods to those pots by leaving food for them there as well.