very strange that mount command doesn't work
try
busybox mount /dev/sda7 /sda7
In dmesg output sda is missing, can not be contacted.
Even more strange is this output in dmesg
[67727.634227] EXT3-fs (sdc7): error: can't find ext3 filesystem on dev sdc7.
[67727.641660] EXT2-fs (sdc7): error: can't find an ext2 filesystem on dev sdc7.
[67727.649206] EXT4-fs (sdc7): VFS: Can't find ext4 filesystem
[67727.655345] FAT-fs (sdc7): bogus number of reserved sectors
[67727.660911] FAT-fs (sdc7): Can't find a valid FAT filesystem
[67727.684165] FAT-fs (sdc7): bogus number of reserved sectors
[67727.689735] FAT-fs (sdc7): Can't find a valid FAT filesystem
[67727.704369] NTFS-fs error (device sdc7): read_ntfs_boot_sector(): Primary boot sector is invalid.
[67727.713265] NTFS-fs error (device sdc7): read_ntfs_boot_sector(): Mount option errors=recover not used. Aborting without trying to recover.
[67727.725765] NTFS-fs error (device sdc7): ntfs_fill_super(): Not an NTFS volume.
[67727.734232] XFS (sdc7): device supports 512 byte sectors (not 0)
did you try to mount sdc7 ?
To see if we have a slot issue, you could take all disks en put sda (the most lefthand side one seen from the back imn slot 2 and run standalone kernel again to see if the dusk is now detected.
Jocko will comment the raid command output