Quick video that illustrate the issue affecting load cell brake pedals when using elastomers and how it can be easily fixed with a commonly available die springs.

stl for the die spring washer: https://www.thingiverse.com/thing:626...
recommended M6 metal washer: ID=6.5mm, OD=18mm, H=1.5mm
recommended die spring dimensions: ID=10mm, OD=20mm, H=32mm
I would suggest trying blue or red, dark green is going to be quite light (and anything less is going to be way too light)
example die spring source (UK, no affiliate): https://www.bergertools.co.uk/Die_Sp...