Unknown journey on recenttraintimes

I've noticed a few times that there's incomplete information on there for past journeys i wanted to check.
An example would be st pancras to Folkestone central 21st October 23:37.
What could be the reason for it being unknown? And if you happened to have a delay repay for that time, how do the train companies verify it if it's showing as unknown for them too? Or do they have information not published on rtt?

Sometimes the Network Rail data feeds will go down temporarily which can mean the open data sites only show partial or no actual times during the outage. The actual running times should still be available on internal industry systems, it is just the public interface that is affected.

Looks like a problem at recenttraintimes.

Try http://charlwoodhouse.co.uk/rail/liverail/train/15174532/21/10/19