I had this exact problem with my IJ playfield.. the left wood siderail cracked and everything. I replaced the cracked one and that has helped a good bit.. I wouldn't say 100% but at least adjusting the loop guides and things I can get the ball to behave better. With the thing bowed like that, I was getting a lot of mode start releases clipping the slings , and outer loops doing the things.. it was trying to tune that out that i realized the wood side rail was cracked.
My suspicion is that there's so many holes punched in that area for the mode start inserts that the playfield is a little weak there and starts to bow.
I had contimplated putting an eyebolt into the bottom of the cabinet and bottom of playfield with a threaded rod between them / turnbuckle to keep it in tension until it either worked itself out or permanently (just a pain to raise the playfield), but just fixing the wood and some ball guide tuning got me into "satisfactory" zone. If I ever pull it out to clear or something I'd look harder at what's going on.