I think their good spell is defined by how far behind they have been for so long. They've come up with a number of positive policies, policies that would benefit most people. The job is, obviously, to get those policies out there, to get people to the point where they know what Labour stand for. For 2 years the story has been Labour are clueless/divided and just about nothing else. Now they've set out some explicit public sector policies it's probably a kind of honeymoon period - just getting them out there is positive.
I would imagine the next stage will be the Tories putting everything into 'wild eyed Jeremy Corbyn's 70s tribute act will cost every single hard working family £3,000 a year', 'figures produced by a respected economist show that...', 'Labour would raid your pension pot...', you know the story. However I think Labour's policies have to actually get somewhere in terms of poll and approval ratings before this counter attack kicks in. Labour are seen as a 'sub-threat' at the moment, but the Tory counter attack will no doubt be primed and ready to roll.
No mention that the 'resistance' progress, etc has gone quiet(for now) a divided party through the chicken coup is the prime reason the LP lost support in the last year.