www.verdenergia.ws/en/product/146/Compo-...COMPO1160306005.html - this Compo bonsai soil. I think I am overwatering the bonsai because I kept the soil constantly wet. I am about to fix this from now on.

I suspect the whites on the leaves could be from the water you mist, some sediments. Mist only when you water the soil, thats more than enough.

You could mist a hundred times, and it still would not make a difference. These tropical trees need at least 80% humidity and even more all day and night . With misting you can not even reach it for a few seconds. It does not make a difference if you mist or not. Cleaning the leaves from dust sometimes is ok, but thats it.

I would guess its root poblem due to soggy, improper growing medium. I say it because when I did not feed my ficuses and they did not receive light during winter, they did not show any symptoms. They did not grow, but did not look uhealthy. On the other hand when I had them in a similar soil mixture as yours, its roots started to rot because it did not have the chance to grow well, as it did not get the dry-wet cycle often enough. The leaves started to look unhealthy, first they lost the shiny, waxy appearance, then started to lose colour and had yellow spots and later they started to fall from the tree. I repotted in a well draining soil mixture and in a few weeks it turned shiny and green again.