CARGOJOCK - I was ten years on the -400 fleet and all before SIA Cargo came into being. Cargo COPs being cancelled is nothing new. Scheduled pax flights will operate with only a very small load, it is a requirement but it is not the same with freight that can be delayed a day, re-routed etc.
We used to get some fantastic COPs with the freighters only to see them either cancelled or curtailed. Arrive in ANC with a COP that takes you to LAX, ORD, JFK, AMS, DXB and home to SIN only to be met by ground staff at ANC with a telex saying that we take min rest and operate back to SIN, via TPE the very next day and that happened more than once.
Freighter COPs were always treated with up most caution as they could evaporate at the drop of a hat - it is the very nature of freight operations.