MD1220 fault state in split mode

I am trying to switch our MD1220 storage vault into Split mode. However, after switching and repowering, the unit stays in fault mode (upper led blinking amber). The unit does work in "normal mode", however on our R740 server connected to the MD1220, iDRAC 9/storage/enclosures says "RAC0501: There are no physical disks to be displayed. 1. Check if the host system is powered off or shutdown. 2. Check if the physical disks are inserted into the enclosure or attached to the backplane." Also, in the Advanced properties of the enclosure page, it is mentioned:

Any ideas to solve this are highly appreciated!