It's possible that the dying canes are two years old, have fruited, an are dying a natural death. Bramble canes have a two year lifecycle.
We can't tell from the photo but it's also possible that there are other plant problems at work- insect pests, diseases, and abiotic problems.
Please send photos of any symptoms you see on the new shoots that emerged this spring- lesions on the stems,, wilting, etc. jt