Liquid mask question

[Ashlandchris]

I tried some liquid mask a few weeks back but when I tried to cut the design I found the mask was too rubbery and wouldn't score smoothly, almost like trying to cut through a balloon. As this was my first try and I was doing ok with masking tape I went back to it and gave up the LM as a bad job.
2 weeks back I bought a second hand car that came with an unpainted, but LMd shell. I decided to try cutting it and it was a joy, so as I need a new shell for one of my buggies I decided to get my jar out once more and I have followed all the correct advice I think - washed the shell, dried it, applied thin coats and let it dry well between the coats. It now has 4-5 coats on nice and even, been drying for 48hrs since last coat and today I tried to cut it and once more the (new) blade just puckers up the rubber
Have I got dodgy LM ? Are there different grades or am I just not doing something right?
Any help gratefully received