I cannot understand this problem.... I have 10 hdd disks (ironwolf 8tb / 10tb) in use and the onboard controller with another 6 disks - all are displayed cleanly. so I suspect a problem with the operating system or the mainboard. It would be helpful to have information about the chipset / operating system. I have a z270 and windows 2016 on it. What did not work was another raid controller - this caused conflicts.

Does your hard drive really have power? i have had problems with various Y cables / loose contact. i have either built all sata connectors directly onto the cable from the power supply unit or soldered the cables to those from the power supply unit. i have also had to restore my backup because too many disks flew out of the raid.

then the problem is already obvious... if the hard disks are not displayed during initialisation, they will certainly not appear in the operating system either... problem seems to be resource allocation
suggestion: deactivate unnecessary onboard resources in the bios (e.g. raid controller), try another slot for the card on the mainboard to see what helps. Could it be your sata cables?
in short, try to run all 10 disks on the controller with minimal hardware and check if you have the latest bios version.