Misting treats the symptom, not the problem. A begonia plantlet doesn’t need more water in the air around it for five minutes twice a day — it needs sustained high humidity for weeks while the plant slowly builds a working cuticle.

You deflasked a begonia, it looked completely fine, and then a day or two after potting it collapsed into a soft, translucent mess. This is one of the most upsetting things that can happen with a rare begonia TC plant, and it is unfortunately also one of the more common failure points with this genus specifically. Here is what is actually going on.