BeginnersLuck

As for your first question, yes, 6k can be re characterized as 6k leaving 12k as pre tax/roth. As for your second question, I would probably consider this missed deferral opportunity in which the employer is required to pay 50% of the missed deferral amount. See link below for further details https://www.irs.gov/Retirement-Plans/Fixing-Common-Plan-Mistakes---Correcting-a-Failure-to-Effect-Employee-Deferral-Elections