The part that surprises people: most scoring problems are shaping problems arriving late.
A score opens because the surface of the loaf is under tension and the cut releases it in one direction. If the shaping did not build a taut skin, there is nothing to release, and the blade is just making a mark on a slack surface. That loaf will bulge and tear wherever it likes no matter how well you cut it.
How to tell which you have: after final shaping, the loaf should feel drum-tight on top and hold a domed shape rather than spreading. If it slumps in the banneton and comes out flatter than it went in, the tension is not there and the score cannot work.
The other thing shaping decides is where the weak point is. A seam that is not sealed properly underneath is a ready-made blowout, and it is usually low on the side: which is exactly where yours is bursting. Worth checking your seam is properly closed before it goes into the banneton.
So the order I would work through it: seam sealed, shaping tight, then the deeper and lower-angle cut described above, then steam. Change one at a time and give each two bakes, or you will not know which one did it.
And for what it is worth: a good crumb and good flavour means the hard parts are already working. This is the cosmetic end, and it is the most fixable.