It could just be a vein that has shot off that way as underneath looks like good veining. I’m 50/50 on it.
If you have seen the embryo moving I would leave it a few more days & recheck. If it is degradation it should show more in a few days.
I had some that looked like that and it was strong veins. When I did get a blood ring it was really obvious. I would leave that and check again. Only done 2 incubation but was confidently told my best chicken was a goner on here. So Glad I kept it in
Usually I only see blood rings ocur in the very start of incubation. Usually they never really start to vein, just form the ring. It looks good to me, but it does look like it may have been incubating upside down.