So after a few prints where nothing sticks (New A350 machine) I can now see the issue.
The bed is nowhere near flat. Calibration probably won’t help.
What have others done to correct this issue? I would have assumed this should have been a precise machined area.
Washers? Shims? What have you done?
Look at the straight edge in the pics.
Those are serious gaps, are you sure you’ve mounted the support frame correctly (hex bolt heads facing downwards)?
Yes those gaps are huge, the centre seems high in the middle in the diagonal, you can feel it if you run a hand over it. Hence nothing sticks.
Thought I had it right. Going to take off the bed today and try to get it flat. May have to add some shims.
Will also email support, in case I have a badly machined frame.
@ronzelver great call, thank you.
It was not the socket nuts, but once I got the heated bed off, I realised I had the whole platform on upside-down. There are 4 inbuilt washers for the linear modules and they were pressing the middle of the heated bed upwards. Hence the gaps.
30 screws later and it’s absolutely flat.
That was exactly my suspicion, good to hear you got it fixed! Happy printing 
