Rocket won't launch

[Two]

I just stumbled upon something I think is a bug, but don't know what or why. I build a simple moon-orbiter, which launched fine the last few times, but now after an upgrade it no longer wants to leave the launchpad, like it is super-glued to it (despite enough TWR). But after some seconds of burning it seems to hit a magical number and suddenly skyrockets upwards (literally).

The first stage launches only the T30 engines.

The problem seems to be related to the total weight. If I remove some parts to make it lighter (even fuel) it launches below a certain weight (22,7t total, launches at about 22,5).

This is technically a modded game, but this rocket only has stock parts.

Mod I use: KIS, KER, MechJeb2, Simple Science Fix, Stage Recovery

[sal_vager]

It's likely the sticky launchpad bug, sometimes colliders get stuck together, if you use decouplers as feet you can avoid it.

[Two]

That probably was it, thanks. I added landing stabilizers to push it up a little and it flew like expected.