Warping and adhesion issues

Ever since upgrading the 3D printer to the Ultimaker 2+ I've had issues with prints warping and detaching from the build plate.

Today I finally twigged what was different between before and after the upgrade. The 2+ kit came with a calibration card for bed levelling.

I've measured the thickness of the card against the thickness of the paper I used to use. The paper is 0.03mm thinner at 0.12mm thick. Not only that but the new coated card has also picked up a thin layer of plastic in places from the nozzle so the thickness is no longer consistent, at one point is was 0.20mm thick compared to the average 0.15mm. The paper, despite having been in use for two years, does not have anything attached to its surface.

I've gone back to my thinner paper calibration and the first print is still attached to the bed.

I do not use any adhesive on my glass. I keep it clean with an imitation chamois leather and very occasionally degrease it with isopropyl alcohol.

I also made a change to the design of the model to add expansion gaps so that the shrinking plastic cannot pull the full width of the model.