The SSD you are currently using may be faulty.
Have you tried reformatting the SSD or using a different SSD?
What method are you using to write a file to it whilst it is taken out?
Please confirm the brand and type of SSD you are using?
Ok, so it is a microSD card...
Have you tried using a different microSD card, particularly a smaller capacity card? - above 8GB is not recommended because although larger cards will still work, they won't work as efficiently and will slow the device down...
Have you tried formatting the microSD card using the Montana?
These cards can wear out and fail over time.
Or the card may have gotten corrupted during the reset.
Or do you have another card you can try?