Hi
I don't know if you've resolved this but i started getting the same problem with War of the Walkers last night (NullReferenceException on EntityNPC.OnUpdateLive).
" 2018-02-08T19:29:42 2000.422 INF Time: 5.95m FPS: 59.94 Heap: 1774.9MB Max: 1813.2MB Chunks: 641 CGO: 555 Ply: 1 Zom: 2 Ent: 5 (15) Items: 0 CO: 1 RSS: 4412.7MB NullReferenceException: Object reference not set to an instance of an object
at EntityNPC.OnUpdateLive () [0x00000] in <filename unknown>:0
at EntityAlive.OnUpdateEntity () [0x00000] in <filename unknown>:0 "
I was on day 16 of a War-of-the-Walkers single-player playthrough, standing in Trader Rekts, when the NRE's started spamming the screen.
Only by moving far away (slowly) did the console errors stop, but on returning to Rekt, the errors started up again.
I think I've solved it. Open the console and do 'le' (list entities). I saw two NPCs (kevin & larry) in the area as well as Rekt. So i killed Larry with 'kill'. After a short period, Larry disappeared from the list of entities, and the null-reference-exceptions stopped.
Maybe this will work for you too.
In terms of versions, I'm running 7Dtd Alpha 16.3 (b8). WOW v5.17.b64 ModSMX A16.3b 12R2
I'd been playing on a Ravenheart multi-player server recently. Maybe the two mod's don't get on ...