"Banking" is kinda vague.
Upon bending a rail into a curve a twist can develop here and there( a ramp/grade if it happen just "wrong"(vs just right) It is from the metal working pulling/stretching, bending, drawing/pinching. Sometimes its the setting, sometimes the sheet variances.
It's hopefully worked out to flat when fitted to ties, but tweaking tube track to get a good flat plane is old school basics. Everyone delivered twisty track at times.
Tweak till flat, hold tight and flat while push-tighteninghe tie tabs slighty. (Mine was flat)
If its comming apart from centrifugal pressure that's common in track too. And as if screws wouldnt work, or the cat stole your screwdrivers. 
...Try a modern track clip....a zip tie 
.
Old school, once any brand track is assembled you should close the loose tube over the opposing rails pins and crimp the new rail onto the pin notches. Screwing it down, sitting on some carpets, track tie clips, or zip strips etc keep you from needing to crimp. I didnt crimp nor fasten them beyound a push and haven't had gaps open. But I'm only running 4 driver steam and 5 pretty light cars.
I do run um "too fast"
