Thank you, so it could be a problem with my controller. I basically have 2/4 IOM6, but whatever I do, I can only see 24 disks in TureNAS Core. Interestingly I can see disks from both my disk shelves at the same time but never more than 24.
Just out of curiosity, what firmware do you run on your controller? I am running "16.00.12.00 - IT-Mode" and tried "16.00.11.00 - IT-Mode" but did not go further down, yet.