NightZombies is having the issue mentioned above, and the developer does not respond, so I attempted to restructure the plugin from scratch. 
I'm not a developer, but my version compiles just the same as NightZombies. 

Unfortunately my version is also failing to pass the configuration values to the game. 

It seems like it always uses the default values. 

https://pastebin.com/Rd8SGFHX

I was wrong. Some of the values work fine but there is still an issue with updating MaxHealth and also an issue with Broadcast settings.

Merged post

I reverted everything back to your original version and chose to focus on one issue at a time. Health is not updating correctly. 

https://pastebin.com/Rd8SGFHX

This version switches to the InitializeHealth method. This is confirmed working to update Health of the zombies upon spawn, but I don't think it correctly updates MaxHealth. 

I set Health to 400 in the config file and now they will spawn with 400. But any type of damage immediately bumps them back down to 200 before regular damage calculation sets in. I don't know how to properly update MaxHealth yet.

Merged post

BTW I did fix the Broadcast settings, but the Health setting is still not fully fixed.

Merged post

I just fixed the Health setting too so that it also updates MaxHealth!

https://pastebin.com/Rd8SGFHX