Hi Drew, thanks for the update.
I went upstairs to get my Macbook (to download your suggestion), opened it and (of course) the SD was gone.
So I opened the browser and started searching for the download you mentioned when suddenly my SD card appeared on the desktop !
Crazy right ? So I closed my Macbook, waited for it to go to sleep, opened it and the SD card was gone but after about 30 sec. it appeared....
Next I downloaded the Transcend tools found the menu option only to see that it was already set to 'ON'.
So this does bring the SD card back to life, but (on my system) it takes about 30 sec... way to long because in the meantime Onedrive already tries to Sync and comes to a halt because the card is missing.
Just out of curiosity I set this option to 'OFF' and closed my Macbook again.
After I let it sleep for a while, opened it and the SD card bas back immediately as soon as the display came to life.
since then I have opened and closed my Macbook several times and every time the SD card was right there on the desktop.
Even did a reboot and sleep, open, sleep, open to test.
I still don't know what it is that I've done, or maybe all this fiddling made it somehow work again.
During the whole proces (earlier that evening) I did install this tool :
http://blog.appgineers.de/post/101608761084/new-advanced-feature-for-nifty-minid rive-users
But couldn't make it work so I deleted it again.
I'm gonna leave it for now, but wanted to let you know that 'somehow' OSX 10.11.5 can seem to work with the SD card.
I will keep checking this thread for updates and if there is anything I can do, let me know !
Cheers ! Richard