_ArrayBuffer crash - ios

Question

It have a crash that I can't reproduce it on my phone. I call this function in DispatchQueue.concurrentPerform.
Here is my code:
public var arrayLessons: [NotesLessonDataModel] = []
...
func addLessonIfNeeded(lesson: NotesLessonDataModel) {
if lesson.isValid() == false { return }
for item in self.arrayLessons {
if lesson.id == item.id {
return
}
}
self.arrayLessons.append(lesson)
}
...
DispatchQueue.concurrentPerform(iterations: array.count) { (index) in
requestGroup.enter()
// Callback function
self.addLessonIfNeeded(lesson: item)
requestGroup.leave()
}
Here is the firebase crash report:
Crashed: com.apple.root.user-initiated-qos
0 libswiftCore.dylib 0x383c88 _swift_release_dealloc + 24
1 Pocket Papers 0x111594 specialized _ArrayBuffer._consumeAndCreateNew(bufferIsUnique:minimumCapacity:growForAppend:) + 4339750292
2 Pocket Papers 0x91bdc PPNotesManager.addLessonIfNeeded(lesson:) + 4339227612 (<compiler-generated>:4339227612)
3 Pocket Papers 0x927f4 closure #1 in PPNotesManager.getLessonsFromSections(_:exam:completion:) + 146 (PPNotesManager.swift:146)
4 libswiftDispatch.dylib 0x5558 partial apply for thunk for #callee_guaranteed (#unowned Int) -> () + 28
5 libswiftDispatch.dylib 0x5584 thunk for #escaping #callee_guaranteed (#unowned Int) -> () + 32
6 libdispatch.dylib 0x4860 _dispatch_client_callout2 + 20
7 libdispatch.dylib 0x18d7c _dispatch_apply_invoke_and_wait + 160
8 libdispatch.dylib 0x18790 dispatch_apply_f + 728
9 libswiftDispatch.dylib 0x54c8 static OS_dispatch_queue.concurrentPerform(iterations:execute:) + 284
10 Pocket Papers 0xa5e7c closure #1 in NoteViewController.requestLessonDetails() + 161 (PPNotesManager.swift:161)
11 Pocket Papers 0xc240 thunk for #escaping #callee_guaranteed () -> () + 4338680384 (<compiler-generated>:4338680384)
12 libdispatch.dylib 0x2a84 _dispatch_call_block_and_release + 32
13 libdispatch.dylib 0x481c _dispatch_client_callout + 20
14 libdispatch.dylib 0x7968 _dispatch_queue_override_invoke + 756
15 libdispatch.dylib 0x15fe0 _dispatch_root_queue_drain + 388
16 libdispatch.dylib 0x167d8 _dispatch_worker_thread2 + 112
17 libsystem_pthread.dylib 0x3768 _pthread_wqthread + 216
18 libsystem_pthread.dylib 0xa74c start_wqthread + 8