I resolved this issue by forcing FMallocAnsi usage on iOS platform.
if (Target.Platform == UnrealTargetPlatform.IOS)
{
GlobalDefinitions.Add("FORCE_ANSI_ALLOCATOR=1");
}
https://alyamkin.artstation.com/blog/9VEQ/ue4-ios-and-pointer-being-freed-was-not-allocated