There has been a lot of updates running, so might be bogged down. I'll give it 24 hours and see if it resolves itself - if no change, will get in touch with support. Thanks so much for your help!
Any luck? Did the campaign end up running?
Unfortunately no - can't seem to get around the skip status unchanged - have a ticket raise with support now...
Check that the lead source field is not blocked for update (in the admin -> field management).
Thanks Greg. I did look at that, but nothing in field management is preventing the update.