First of all, I can feel your frustration! I'm trying to think a way out of your dilemma.
I could not understand why the glass would be so warped and bowed, but after reading
this link I have a much better understanding. I cannot see that the chinese manufacturers would specify any extra special flat glass.
Are you using a cutting mat? Rollsroller come with a softer, more rubbery type of cutting mat that I suspect would 'soak up' some of the variations in the glass surface. I do have a feeling that Rollsroller would be much more picky about the glass they are supplied.
Are you using enough pressure on the roller? Rollsroller use 6 -8
bar / 87-116 psi. We have ours set to 8bar at all times.
Other than that, I can only suggest that you keep shimming the glass and hopefully you will have some workable solution.
I'd disconnect and throw that heater thing in the bin. Probably electrocute someone, explode the roller (no joke) or burn your shop down overnight.
It must be very disappointing. I could rave on and on about buying chinese stuff, we all do it or at the very least are tempted, but deep down we all know the story...our worst fears are almost always realised.
At least they are consistent.
PS
Are you applicating acm, acp, boards etc or are you laminating prints and vinyl in pics and video?
These things aren't ideal at all for laminating, they are more for applying app paper, app papered cut vinyl to boards or banners, laminated prints to boards or 'floodcoating' a board with coloured vinyl etc.
Even a Rollsroller can badly wrinkle paper backed vinyl just by running the roller over it. We've never use ours to laminate a print (well, maybe something very small). We use our laminaters to laminate and the Rollsroller to applicate.