While this always has been a potential problem, I find it occurring more regularly these days.
The problem is a mismatch between the airfoil thickness on the actual wing versus the thickness on the fuselage- that is on the outboard edge of the fillet that should join to the airfoil.
It seems more and more the case that the thickness of the wing is less than allowed for by the fuselage fillet. If one merely putties the bump, one produces a fillet that goes out on the wing farther than it should. Grinding of the portion on the fuselage is required- a very difficult job.
Why is this happening? I am wondering if the upper wing sections are flattening out after the kit is produced. This would give that effect. Even some mfgs with very expensive prices and an otherwise good reputation are putting out kits with this problem.
Seems to me there could be a stub spar molded into the upper and lower halves of the wing to hold the thickness.