A paying agent is just that, an "agent", and significantly, an agent of the plan, not the participant. As such funds held by the paying agent still belong to the plan until properly disbursed to a participant. So the paying agent is likely correct. But paying agents typically have a time-lag, they need to insure they've received good funds before disbursement, plus you throw in the holidays and the normal year-end crush to get plans distributed and paying agents are very busy in December. They will usually communicate a cut-off date for distributions to be made by 12/31. I would imagine their cut-off date was well before 12/26. And given that 12/26 was a Saturday, wire transfers normally don't occur on weekends and bank holidays, so that would make it 12/28.
So it really comes down to communication. Did the paying agent represent that it could be paid out by 12/31? Did the paying agent advise its cut-off date for year end distributions? Did the plan or TPA communicate to the paying agent the need to rush this one thru by 12/31? Did the plan communicate any sort of timing deadline for requesting a CRD?
Seems to me the paying agent turned this around really quickly given that 1/4 was only the 4th banking day after 12/28. It really comes down to what was communicated such that all parties would have proper expectations and be able to plan accordingly.