If this is really true, then my opinion of Thailand just dropped several levels. Is „medical emergency“ really the reason they expect you to have 800k? Why would you ever need it for a medical emergency? Any reasonable person has an insurance that covers medical emergencies and costs much less than 800K...
I dont understand why or how they could even ask you to show 500K after 180 days. As far as I know there is no rule that requires you to keep the 500K locked in your account for 180 days or even longer. If there is, please enlighten me.