I just wanted to chime in and let you know that you’re not alone with the panda woes.
About a decade ago I got my first batch of panda corys and they were bullet proof and bred quite a bit in my community tank.
About a year ago I got a new tank and decided I had more space for a larger group of them. I bought some pandas from multiple places, local and online, and none survived very long. Some didn’t make it through QT, others slowly stopped eating and would die after making it through QT and into my main tank.
It was quiet frustrating since my original pandas were thriving the whole time. I’ve since stopped trying to add new pandas and have been encouraging the others to breed to increase my group.
One interesting thing idea I came across going through this last year, was that many pandas probably are just too overbred/inbred and overuse of antibiotics at fish farms overseas.
Hopefully your guys make it through the meds. Good luck!