Are you standing still when the radar shows they're close, because I had a similar issue, but found if I stood and waited that the signal grew weaker and was able to move with no issue again.
Viewing post in Third Crisis (Free Version) comments
I just finished the game today, with a lot of retry of course. Even when I'm standing still the radar would still go off and I would die instantly. I used noclip on console command to make it easier but it seems the shadow people could still reach me even when I'm through the wall. All in all, I'm good now.