I really have no idea what you're talking about. Of course it shows up. I'm not sure what gave you the idea that it doesn't. It's a regular transfer in and out.
That would be a question for your local immigration office. Not every office allows conversions to non-O. For the offices that do, they each have their own requirements. You should go there and ask if they allow it and for their printed list of requirements. The primary thing is going to be proof of 800,000 baht that's in your Thai bank account for 2 full months already and that you can show was transferred from overseas.
Why would the bank delete it? It's not in the transaction history that immigration gets. They get a bank statement that shows 800,000. That's all they care about after receiving their extra money to make sure that's all they care about.