VS201 late last few days

Anyone know why the VS201 has been late leaving most days this week? Yesterday 1 hour late day before 1 hour late and I think day before that 4 plus hours late.
I note for Wednesday 8 and Thursday 9 the incoming Syndey flight arrived on time.

Perhaps this?

It can be down to route restrictions or that it was going to be a short flight time & would have arrived at LHR too early.