*Second posting for increased visibility*
I have taken the issue I am about to describe to Nintendo Customer Support at the Redmond, WA headquarters, but I wanted to seek more information here while waiting for them to get back to me. Because the escalation supervisor team in Redmond noted further contact may take approximately two weeks, stating they will be contacting NCL personnel in Japan, I thought it'd be a good idea to see what guidance members on this forum may be able to offer in the meantime.
For the past year-plus, I have been using one of the Nintendo-approved external hard drives with my Wii U Basic console (Western Digital My Book Essential 1 TB) to store downloaded titles and game save files, and have never had any problems. However, immediately after I installed the latest system update, the Wii U began treating the drive as though it had never been connected to it before. It displayed the following prompt, as though it was the first time I was connecting the drive!
"You have connected a USB storage device that has not been set up for use with this console. Do you want to format the device so that it can be used with this console? Please note that this will delete all data currently saved on the USB storage device."
All of my game saves and downloaded titles are still there, but are now inaccessible following the update. If anyone has any solutions, or is experiencing the same problem, I would love to hear from you! Thanks!