Not sure why they are reported as different sizes, but in the syslog I see
Jul 31 18:46:46 Tower kernel: mdcmd (1): import 0 sdc 2048 1953513560 0 Samsung_SSD_860_EVO_2TB_S597NJ0NB20380F
Jul 31 18:46:46 Tower kernel: md: import disk0: (sdc) Samsung_SSD_860_EVO_2TB_S597NJ0NB20380F size: 1953513560
Jul 31 18:46:46 Tower kernel: md: disk0 new disk
Jul 31 18:46:46 Tower kernel: mdcmd (2): import 1 sdb 64 1953514552 0 Samsung_SSD_860_EVO_2TB_S597NJ0NB18397B
Jul 31 18:46:46 Tower kernel: md: import disk1: (sdb) Samsung_SSD_860_EVO_2TB_S597NJ0NB18397B size: 1953514552
Jul 31 18:46:46 Tower kernel: md: disk1 new disk
which suggests they are not exact;y the same size. You could try swapping them over and see if UnRaid then lets you start the array.