Bow twist can be due to limbs being miss-aligned, twisted, badly seated, loose fixing bolts or even a damaged handle.
This twist can be checked on a strung flat bow by using two arrows. Each arrow is slipped between the string and limb at each end of the bow and set square with the string.
The limb alignment is verified by looking down the full length of the string from one end of the bow. Both arrows should be parallel to each other and not crossing when viewed from the end position.