The width of the V will reduce the area's strength, but just proportionaly to the degree of the material removed. If material is taken off the back (target side)it can be really serious the face (side you see when shooting) is the best area for thinning the limbs, but obviously wouldn't increse the cam clearance. The key issue is whether the widening was done in a very smooth maner, otherwise there could be a stress riser. Presumably the factory believes that what is being done here consists of moving the bow towards factory specs for this model and cam. That would be just fine, but I don't have that much confidence since you seem to imply that the string is already wearing again. In which case the job didn't restore factory specs (so how good a job was it), those specs don't work (unlikely?), or something else is also wrong like a burr on the cam or whatever. If you want to persue remediation, then one option would be for you to ask the factory to provide you with factory specs. How wide, how thick, what are the dimension of the cutout. I don't know how much fitting of the limbs they do at the factory, but depending on their process, not all limbs will be indentical due to tiller and weight issues, but the cut-outs maust have some minimal specs. If you have calipers amoung the family treasure you could do your own measurements to see what gives.