firebase-ios-sdk: Every time after app update cannot receive FCM token after first run only

• Xcode version: 10.2.1
• Firebase SDK version: 5.20
• Firebase Component: Messaging
• Component version: umm, it’s a binary from iOS SDK 5.20

[REQUIRED] Step 3: Describe the problem

Steps to reproduce:

I call [FIRApp configure]; in application didFinishLaunchingWithOptions. Then, when when user goes to in-app settings, (s)he wants to enable or disable remote notifications for my app. I need FCM token to send it to server and check. I use

[[FIRInstanceID instanceID] instanceIDWithHandler:^(FIRInstanceIDResult* _Nullable result, NSError * _Nullable error) {
			if (error != nil) {
				//NSLog(@"Error fetching remote instance ID: %@", error);
				token = "error";
			} else {
				//NSLog(@"Remote instance ID token: %@", result.token);
				token = [result.token cStringUsingEncoding:NSUTF8StringEncoding];
			}
			gettokenstarted = false;
		}];

and return token.c_str();. It works fine… Well it actually fails… only every time… after user gets an update for my app. User installs an update and runs app, then instanceIDWithHandler called but somehow it’s callback doesn’t called, neither error nor token are returned. Workaround is close app and run it again. From second run it works, but on next update it happens again… It’s PITA. Please tell me if You have some workaround, or how long do I need to wait until it fixed? I have it for 3 months already since I migrated to FCM. Android version works fine, but on iOS some strange things happening here.