Might not be 3M but some "cheaper" alternative. It'll take a lot for real 3M VHB tape to come loose on it's own from a windscreen. Maybe the screen wasn't cleaned properly before it was attached.
Edit, I've just noticed you attached to the dash rather than windscreen, that's a different story then. I'd buy some more 3M pads and reattach but it's worth giving the dash a good clean first.