I'm not really familiar with "Rave" and how they have everything set up, I was giving you the 2 main goto files to look in.. I know they have a discord set up and it might be your best option since everything can gone through on the spot. It kinda looks like, just from what you posted, its that you may have an entity issue of some type. Could be in the entityclasses.xml could be entitygroups.xm or could be gamestages.xml. Or it could just be you have some files that didn't take when you d/l it and all that.It looks fine in the xml... then again, I'm not exactly sure what I'm looking for that's out of place.
Deleted game mod from ModLauncher (I even uninstalled all of modlauncher and then reinstalled it just in case). Load everything back up, and then load up my saved game.
Once I load in, I'm in an empty biome. Walk around a little bit just fine, but once the game tries to spawn some zombies, I get all kinds of errors. This makes me think it's a general spawning issue and not necessarily a WolfGroup specific issue. I don't know what's going on at this point - I have exceeded my programming and debugging skillset, unfortunately.
More snippets of my output file mainly to show that it's not just WolfGroup
Code:2018-03-27T18:35:47 198.952 INF Spawning sleeper zombie from sleeperHordeStageGS110 NullReferenceException: Object reference not set to an instance of an object at EntityGroups.GetRandomFromGroup (System.String _sEntityGroupName) [0x00000] in <filename unknown>:0 at SleeperVolume.WW (.World ) [0x00000] in <filename unknown>:0 at SleeperVolume.Tick (.World _world) [0x00000] in <filename unknown>:0 at World.OMQ () [0x00000] in <filename unknown>:0 at World.OnUpdateTick (Single _partialTicks, ArraySegment`1 _activeChunks) [0x00000] in <filename unknown>:0 at GameManager.JQ () [0x00000] in <filename unknown>:0 at GameManager.Update () [0x00000] in <filename unknown>:0 (Filename: Line: -1) 2018-03-27T18:35:48 200.303 INF No valid sleeper spawn locations were found, they are either all visible or are in solid space. Marking volume as cleared. 2018-03-27T18:36:08 219.902 INF Time: 1.87m FPS: 60.00 Heap: 1111.7MB Max: 1111.7MB Chunks: 756 CGO: 666 Ply: 1 Zom: 0 Ent: 3 (3) Items: 0 CO: 1 RSS: 11457.2MB 2018-03-27T18:36:16 227.869 INF Disconnect 2018-03-27T18:36:16 227.877 INF NET: Stopping server protocols 2018-03-27T18:36:16 227.884 INF NET: UNET server stopped 2018-03-27T18:36:16 227.942 INF NET: Untiy NW server stopped 2018-03-27T18:36:16 227.942 INF [steamworks.NET] NET: Server stopped 2018-03-27T18:36:16 227.943 INF [NET] ServerShutdown 2018-03-27T18:36:16 227.944 INF SaveAndCleanupWorld 2018-03-27T18:36:17 228.546 INF Saving 386 of chunks took 383ms 2018-03-27T18:36:17 228.552 INF [steamworks.NET] Stopping server 2018-03-27T18:36:17 228.575 INF [steamworks.NET] Exiting Lobby 2018-03-27T18:36:17 228.595 INF World.Unload 2018-03-27T18:36:17 228.701 INF Exited thread thread_GenerateChunks 2018-03-27T18:36:18 229.595 INF Exited thread thread_Pathfinder 2018-03-27T18:36:18 229.596 INF World.Cleanup 2018-03-27T18:36:18 229.609 INF Exited thread thread_Regenerating 2018-03-27T18:36:18 229.609 INF Exited thread HQ 2018-03-27T18:36:20 231.504 INF Persistent GamePrefs saved 2018-03-27T18:36:20 231.504 INF Cleanup 2018-03-27T18:36:20 231.505 WRN Missing cleanup for XML: sounds 2018-03-27T18:36:20 231.518 INF AchievementManager.Cleanup 2018-03-27T18:36:20 232.134 INF OnApplicationQuit
I would probably jump on their discord and see if they are around, so you can get someone to go through it faster and on the spot.

Hope it works out for you!