Don't know if this is useful, but I just had an NRE (solo game). I was upgrading blocks to concrete (with a multitool so pretty fast) when a wandering horde spawned in. Aside from the console window popping up, the NRE didn't appear to cause any harm (well, that I'm aware of at this point, at least). The horde behaved as expected too.
Don't know if rapidly upgrading blocks at the same time as the horde spawned could maybe just have caused a minor glitch.
First NRE in the 108+ hours this game has lasted so far (day 54, level 152, so I've seen and done quite a lot without problems).
2024-06-15T12:46:42 1980.059 INF AIDirector: Spawned wandering horde (group bloodHordeStageGS99, zombie [type=EntityZombieCop, name=zombieFatHawaiianFeral, id=19635])
NullReferenceException: Object reference not set to an instance of an object
at ChunkGameObject.StartCopyMeshLayer () [0x0002e] in <a58aca9c8ed54d639b41f6dc2ac2f31b>:0
at ChunkManager.doCopyChunksToUnity () [0x00193] in <a58aca9c8ed54d639b41f6dc2ac2f31b>:0
at ChunkManager.CopyChunksToUnity () [0x00000] in <a58aca9c8ed54d639b41f6dc2ac2f31b>:0
at GameManager.gmUpdate () [0x0036e] in <a58aca9c8ed54d639b41f6dc2ac2f31b>:0
at GameManager.Update () [0x00000] in <a58aca9c8ed54d639b41f6dc2ac2f31b>:0
2024-06-15T12:46:43 1981.110 INF AIDirector: Spawned wandering horde (group bloodHordeStageGS99, zombie [type=EntityZombie, name=zombieJanitorRadiatedWeak, id=19636])
2024-06-15T12:46:43 1981.155 INF Chosen Random Zombies: 26
2024-06-15T12:46:43 1981.155 INF Spawned 26 Random Zombies
2024-06-15T12:46:43 1981.155 INF AIDirectorGameStagePartySpawner: groups done (1)