I can finally report that I fixed it. What I did to resolve my issue tried to determine if it is a hardware/software failure connected 8 disks to 1 HBA (HBA2 was not installed at that time) and checked if every disk was listed (computer management in windows server 2016, another OS would probably work as well) unplugged HBA1 and connected HBA2 -> also checked if 8 disks were listed -> one disk was missing, so I checked all connectors and one was loose.
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