Unfortunately, I think you have another faulty device. I can only think of two things.
The first is a manual factory reset. I'm not sure if that is what you mean by "reset attempts". If not, try the method on
https://wiki.mobileread.com/wiki/Kob...Aura_Edition_2.
The only other thing is to open the device and replace the internal micro SD. It's the only replaceable part in the device and problem like described might be a failing card. Of course, opening it will break the warranty, but it might be preferable to sending it back.