This issue has happened twice to me after I got the 14.13 update.
First occurrence: In Run activity, the watch screen was frozen on the performance update screen. I had a +2 performance and it stayed there the whole time until I stopped and saved my run. I was unable to get back to my default Run data screen.
Second occurrence: While running, when I reduced my pace to a walk, the activity auto-paused (incorrectly). Then when I hit resume, the watch face stayed stuck on the "paused" screen. I could hit Back and get to my default data screen where I could see that the activity was actually unpaused, but the screen would again switch back to the paused screen in few seconds. I had to just assume that the run was being recorded while the watch face showed the paused screen for the last 2 miles of my run.
These screen freezing issues can cause anxiety if I were recording a run for a critical race event. Please try to reproduce this issue and fix it.