It's like a observation of unforecast fog or thunderstorms at the field. Until someone puts out an amended forecast that's the only information we've got to give you.
I think you might be confusing Metron with MAESTRO - Metron does the off block times & ground delays, MAESTRO does the sequencing.
Unexpected traffic holding is often due to a reduction in runway capacity - too much crosswind for LAHSO or the acceptance rate has to be reduced due to strong winds.