Plugin not working after adding custommap

Hey, i know you dont want to give support for custom maps, but i need help because the plugin isnt working after i loaded in my custom map.

I get this error code when choosing my arena map:

Exception while calling NextTick callback (InvalidOperationException: Collection was modified; enumeration operation may not execute.)
at System.ThrowHelper.ThrowInvalidOperationException (System.ExceptionResource resource) [0x0000b] in <fb001e01371b4adca20013e0ac763896>:0
at System.Collections.Generic.List`1+Enumerator[T].MoveNextRare () [0x00013] in <fb001e01371b4adca20013e0ac763896>:0
at System.Collections.Generic.List`1+Enumerator[T].MoveNext () [0x0004a] in <fb001e01371b4adca20013e0ac763896>:0
at System.Linq.Enumerable+<OfTypeIterator>d__32`1[TResult].MoveNext () [0x00067] in <351e49e2a5bf4fd6beabb458ce2255f3>:0
at Oxide.Plugins.SurvivalArena.ArenaSpawned () [0x00193] in <2202a6b27b7e4305be9ac1c99b13720b>:0
at Oxide.Plugins.SurvivalArena+<SpawnEntities>c__Iterator1.<>m__0 () [0x00000] in <2202a6b27b7e4305be9ac1c99b13720b>:0
at Oxide.Core.OxideMod.OnFrame (System.Single delta) [0x00051] in <bae5f1223fce49c493b01571c99dce02>:0

I dont know how to fix this issue, maybe you could help me with that?

EDIT: The Cusom file is attached.

CustomArena.json

Nevermind. you can close, fixed it