The rank that the cheevo is one for anyone who had ranks before it was introduced is one less than the actual rank while for anyone who had got theirs after don't suffer from this bug.
Can bug be dulipcated
yes
if so explain
1) Look at any account that had ranks before the cheevo came in. 2) see that the rank of the person and the rank on the cheevo are apart by one 3) Check any account that got the ranks after the update and see that their rank and cheevo match perfectly.
If you want to get anything fixed at this point, I would highly suggest that you try to make the bug report as clear as possible. Use screenshots if you have to, use the actual name of an achievement or give a specific example.