How to prevent Firebase Query Crash, EXC_BAD_ACCESS (KERN_INVALID_ADDRESS) on App Startup?

Question

I am experiencing this crash on one specific line of code, in one specific method, within the first 2 seconds of the app openning.

This crash occurs randomly on my users devices and never on mine so I cannot reproduce it. I just have what Firebase Crashlytics provides.

---

Some extra details about the code:

• This query is run in ViewDidLoad on the first page the user sees when they open the app

• This query is run in a background thread

• This query is run concurrently with 6 other queries each on their own background thread

• This crash only occurs in this specific query in this specific line

• This crash usually occurs on the first iteration of FIRDocumentSnapshot but occasionally occurs after multiple iterations

---

Some solutions I've already tried:

• I've tried allowing this query to finish before running any other queries

• I've tried running this query last, after all other queries have finished

• I've tried adding NULL checks to snapshot, doc, and doc.data

• I've tried checking for an NSError

• I've tried running it on the main thread

---

Crash occurs on this line when accessing doc.data

NSLog(@"Test %@", doc.data);

---

dispatch_async(dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0), ^{

   FIRFirestore *defaultFirestore = [FIRFirestore firestore];

   [[[[defaultFirestore collectionWithPath:@"Homes"] documentWithPath:homeID] collectionWithPath:collection] getDocumentsWithCompletion:^(FIRQuerySnapshot * _Nullable snapshot, NSError * _Nullable error) {    
       if (error == nil) {    
          for (FIRDocumentSnapshot *doc in snapshot.documents) {    
             if (doc != nil) {           
                 NSLog(@"Test %@", doc.data);            
             }    
          }    
       }    
   }];    
});