Please help: Warping on the corners of my prints with Wham Bam flexible PEX bed

[Grafistole]

Hi there!

I am experiencing some warping issues on my prints at the moment, and I can't seem to solve them. I searched for solutions online and re-calibrated my printer three times but the issue is still there.
A few days ago, I changed the stock bed of my creality CR10s-pro (v1) for a Wham Bam flexible PEX bed. I installed it following the tutorial on the Wham Bam website, being careful to prepare the PEX with steel wool as best as I could as well as cleaning it with IPA and all seems good.I calibrated my printer and ran a few "first layer test" prints with black, GEEETECH, PLA filament, which I had used without issues before I changed my bed.
Although the calibration test prints were great, the following ones had quite severe warping on the edges. After ten or so layers, the corners of the prints start lifting from the bed. The print continued fine and still well-stuck in place, but it was quite ugly on the bottom. I tried solving the problem by re-calibrating and cleaning the printer and lowering the nozzle in order to "squish" more the first layer.

I print with the nozzle at 190C° (210C° for the first layer) and the bed at 70°C.

I don't know what to do to solve that issue.Does anyone have an idea that might help me?The picture attached is one of the back of one of my prints.
Thank you very much.