I have the same issue with you. but when i try to add a new sequencer which is a very simple one in 4.13 UED, it works . I think the issue is about my sequencer because it is converted from matinee from the 4.10 version or even ealier. then I try to delete some camera cuts of my sequencers, it’s works too. so I have to remake the broken parts. in my advise, you’d better make some new sequencer in latest version. Hope that’s may be helpful