That's not a repeating row ID - it's @{pbd_safe}. It looks like you're using the variant proficiency rule, which suffixes cs0cf0 to the roll to stop the sub-result from crit-colouring the final result. Otherwise you'd get, for example, a green crit coloured result from rolling a 2 on the d20, and a 6 on the proficiency d6. A repeating row ID, for reference, is the same as a character ID or any other Roll20 UUID (well... there's some very minor variations) - 20 characters from [ A-Z a-z 0-9 _ - ], always starting with a dash.