I don't do vase culture for anything, nor do I grow vandas, so maybe someone will chime in.

This happens sometimes - the experience I have is with sphag and bag, which is often 50/50 for me. Sometimes the plant recovers, and other times it just gets moldy! It's probably warmth, light, or just a prevalence of spores at the particular time of year...since we are talking about enclosed containers (in other words no air movement) this isn't too surprising, but it is unfortunate and gross.

Try spraying with hydrogen peroxide. I'd keep it out of the bottle for now...

Carol in Ontario grows these in a zone that is only a bit cooler than yours and I believe she has them just hanging out in baskets.

Your plant is Aeridovanda Kinnaree and i do not think it will survive in a soda bottle.
Have you got a humidity gadget to get the readings in your house. In my opinion all this humidity stuff is overdone. Sweat on the brow, jungles and all that stuff.
There are two Phals in bloom in this room and though they are not the greatest phals you will ever see they are blooming. According to the humidity gadget the temperature is 23C and the humidity is 40%.
Outside is worse 23C and humidity 34%. Glasshouse is 24C and H still 40% but i am not growing tropical lowland plants in there.
You need advice from the locals.