I recently switched to experimental. This wasn't happening in stable. Some fences are impossible to vault over, others are fine. There was a knee high fence (or slightly above maybe, but definitely something i jumped over before) i ran towards it and pressed V as usual but my character didn't even try to jump. i toggled walk, and try that way and character didn't try to get past it. I went around and find an opening. doesn't happen on every fence. It can be difficult to reproduce, but happened to me way often.