Hello jetta!
yes it is like CrypticGirls says.
First (I had to laugh a bit sorry), it's called "Fight for your Life", not "Run...", as you can't run not even move anymore.
It's another mechanic from the Borderlands-Game I tried to adopt for this Mod.
https://borderlands.fandom.com/wiki/Crippled
Now the Mechanic might not yet be fully fleshed out, as this Mod is still in early Development.
In the next version there are two changes made:
1) You will still be able to move very slowly so you can try to move a bit (especially around corners) when there is no Zombie or Animal around you.
2) There will be a very expensive and very rare "Adrenaline Shot" medic which will bring you back into life, for the case when there is no other Zombie or animal around
But for the majority of cases,
you need to kill SOMETHING, either a Zombie or an Animal.
Health packs do not help you in this case.
Hope this helps.
(for your example you gave,
this can be a timing problem of these involved Buffs.
The probem is when Buffs activate and trigger, there is mostly a 2 second interval where this happens every time.
So when you kill something with only 1 second left on your "Fight for your life" timer it "can" be it does not trigger it in time.
I will try to find a Solution to this.)