I know a lot of vets seem to condone severe wing clipping, but I am of the opinion to request your vet only clips the first 7 or so primary flight feathers from one or both wings — and that is more than sufficient to keep your bird from flying away or flying into danger.
Regarding molting, there are a few factors that could be involved here — diet, boredom, environmental, behavioral and sickness — and the only real way to determine the cause is to watch your bird for clues and some trial and error.
One thing to consider though, since you have said your bird is a juvenile still, it might be just a little bit too aggressive with it’s own preening while it is still learning to clean itself. To see this is easy — just give the bird a soft splashing of water and watch how the bird reacts. If you hear the bird making excessive noises when preening after being wet or if you notice feathers coming out, then this is the cause.
The diet and boredom are the easiest points to address. For boredom, first try to introduce a new toy that encourages the usage of the birds beak in search of a treat — similar to the treat egg toy I have posted in this story. For diet, simply follow the guidelines in this story as well and if diet is the issue, it will take only a few days to see the difference. I would make sure your bird also gets access to some seeds, even sunflower seeds — but not too many.
Regarding any sickness, take a look at your bird for any obvious and visible signs firstly. Make sure your birds droppings are not watery. If the bird is not eating or the food it is eating is making it sick or sleepy, then diet might be also making the bird feel not so great. Check the birds feathers for any small red mites or any bite/scratch marks in the birds skin at the base of the feathers. If you notice any mites, you will need to apply a topical spray as described in Part One of my FAQ to help eliminate the mites. If you still think your bird might be sick, take it to a vet, perhaps a different vet in your case because you don’t seem too pleased with the advice you have received.
If the issue is behavioral, it could be related to the amount of attention the bird receives — so try to even just talk and praise the bird more if you are not in a position to confidently handle it. For environmental issues, the location of the cage and the amount of sunlight and darkness it receives is really critical. If your cage is not next to natural sunlight, definitely try moving the cage as close to a window as you can and make sure it can hear the birds outside and “smell the breeze”. If the cage is not covered at night, your bird might not be getting sufficient sleep and this will cause issues too. Other household factors which could cause issues would be if the cage is near a kitchen or an area of the home with a lot of fumes or even if there are smokers in your house.
Good luck. Let me know if you figure out the issue — and in case you missed it, Part One of the FAQ is here: https://medium.com/@gwobcke/the-galah-australian-rose-breasted-cockatoo-faq-80f54ed1ab12