You just stated in your question the exact answer as to why you can no longer read the card, and actually won't be able to.
You had it as "Internal" storage, removed it and then "Reset" the device.
The SD card, when made to be "Internal" storage was encoded. Making it only work with that device and only work with the device as it was. When you reset the device, it would have removed the data on the phone itself that connected it to the encoded data on the SD card.
Once that is gone, so is access to the data on the card. For good.
This one of the reason I personally always tell people to back up data from a phone or tablet to a computer or cloud account. Regularly.