GCD TSAN issue: Data race in generic specialization <Foundation.UUID>

The XCODE TSAN thread analyser is throwing up a threading issue:

Data race in generic specialization <Foundation.UUID> of Swift._NativeSet.insertNew(_: __owned τ_0_0, at: Swift._HashTable.Bucket, isUnique: Swift.Bool) -> () at 0x10a16b300

This only occurs in a release build, and its Data race in generic specialization that has my attention.

It pin-points the addID function. But I cannot see the issue. Here is the relevant code snippet:

final class IDBox {
	

	let syncQueue = DispatchQueue(label: "IDBox\(UUID().uuidString)", attributes: .concurrent)
	
	private var _box: Set<UUID>
	
	init() {
		self._box = []
	}
	
	var box: Set<UUID> {
		syncQueue.sync {
			self._box
		}
	}
	
	func addID(_ id: UUID) {
		syncQueue.async(flags: .barrier) {
			self._box.insert(id)
		}
	}
}