Firstly, Woodlice don't eat the growing parts of plants. They are nature's dustmen and are actually surviving on the dead and rotting material such as fallen leaves that quite naturally occur on even the healthiest plants.
Secondly, seedlings should be allowed to grow on in pots or a nursery bed somewhere sheltered out of full sun, watered well and left undisturbed until next spring, when they will be big enough to join the garden. Perhaps the GH is too hot?
Thirdly, and most importantly, slugs and snails are the cause of your nibbled flower buds, if my personal experience serves me well. Lupins are a favourite dinner and as much as you think you are dealing with the problem, evidently some slugs are managing to avoid your methods of control.
I would heap grit onto the crown of the plant in a diameter that equals the outer most leaf touching ground, in the case of Lupins which are mostly upright, this shouldn't be too tricky. But slugs and snails hide inside the rosettes where the flower buds are forming, the same as with Eremurus (Foxtail Lily) and Kniphofia (Redhot Poker) and you must be vigilant at this time or you will have no flowers to speak of, let alone much plant left.
A small sprinkling of blue pellets will help matters if that idea doesn't offend you and you might also try some late night slug runs with a torch and/or garlic spray on the leaves and buds until the problem is within normal bounds.