What I was afraid of. Windows on sda saw the efi on sdc and installed its boot files to that drive. So sda would never boot on its own. But it still should work.
I do not see that boot repair fixed it by adding a chain load entry. We can manually add if if necessary, but I think the partition table error on sdb is still confusing things.
Somehow your sdb2 starts after its end? And starts after the start of sdb3.
Did gparted do that?
Partition Start Sector End Sector # of Sectors System
/dev/sdb1 2,048 2,147,485,695 2,147,483,648 Data partition (Windows/Linux)
/dev/sdb2 2,147,485,696 2,010,161,151 -137,324,544 Data partition (Windows/Linux)
/dev/sdb3 2,010,161,152 2,639,306,751 629,145,600 Data partition (Windows/Linux)
/dev/sdb1 overlaps with /dev/sdb3
/dev/sdb2 overlaps with /dev/sdb3
And update your copy of Boot-Repair. Yesterday Yann was making some fixes on UEFI finding Windows. I do not know his versions, so you may have an older copy.