What happened?

Hello, occasionally we receive crash reports like the one below from our live game. We obtain these reports through Firebase Crashlytics.

> Fatal Exception: realm::KeyNotFound
No object with key '-1' in 'flx_subscription_sets'

It seems that the occurrence of this error is causing a crash in another thread. Details of the crashed thread are as follows:

> Crashed: com.google.firebase.crashlytics.ios.exception
SIGABRT ABORT 0x00000001e15e9198
0 FirebaseCrashlytics 0x1eea8 FIRCLSProcessRecordAllThreads + 184
1 FirebaseCrashlytics 0x1f288 FIRCLSProcessRecordAllThreads + 1176
2 FirebaseCrashlytics 0x164dc FIRCLSHandler + 48
3 FirebaseCrashlytics 0x111e4 __FIRCLSExceptionRecord_block_invoke + 92
4 libdispatch.dylib 0x64780 _dispatch_client_callout + 16
5 libdispatch.dylib 0x46a50 _dispatch_lane_barrier_sync_invoke_and_complete + 52
6 FirebaseCrashlytics 0x101f0 FIRCLSExceptionRecord + 204
7 FirebaseCrashlytics 0xff00 FIRCLSTerminateHandler() + 588
8 libc++abi.dylib 0x13424 std::__terminate(void ()) + 12
9 libc++abi.dylib 0x15da0 __cxa_get_exception_ptr + 30
10 libc++abi.dylib 0x15d60 __cxxabiv1::exception_cleanup_func(_Unwind_Reason_Code, _Unwind_Exception*) + 130
11 realm-wrappers 0x29d0f8 realm::ClusterNode::get(realm::ObjKey, realm::ClusterNode::State&) const + 300
12 realm-wrappers 0x3a734c realm::Table::get_object_with_primary_key(realm::Mixed) const + 180
13 realm-wrappers 0x260244 realm::sync::SubscriptionStore::get_mutable_by_version(long long) + 200
14 realm-wrappers 0x1e2ae4 realm::sync::SessionWrapper::on_download_completion() + 364
15 realm-wrappers 0x22fed4 realm::sync::ClientImpl::Session::receive_mark_message(unsigned long long) + 360
16 realm-wrappers 0x22c4e0 void realm::impl::ClientProtocol::parse_message_received<realm::sync::ClientImpl::Connection>(realm::sync::ClientImpl::Connection&, std::1::basic_string_view<char, std::_1::char_traits<char>>) + 248
17 realm-wrappers 0x236350 realm::sync::ClientImpl::Connection::WebSocketObserverShim::websocket_binary_message_received(realm::util::Span<char const, 18446744073709551615ul>) + 148
18 realm-wrappers 0x21ab64 (anonymous namespace)::WebSocket::frame_reader_loop() + 136
19 realm-wrappers 0x20dba0 realm::sync::network::Service::BasicStreamOps<realm::sync::network::ssl::Stream>::BufferedReadOper<realm::util::UniqueFunction<void (std::__1::error_code, unsigned long)>>::recycle_and_execute() + 220
20 realm-wrappers 0x2144d4 realm::sync::network::Service::Impl::run_impl(bool) + 388
21 realm-wrappers 0x2059f8 realm::sync::websocket::DefaultSocketProvider::event_loop() + 220
22 realm-wrappers 0x2076c4 void* std::1::*thread_proxy<std::*1::tuple<std::*1::unique_ptr<std::*1::*thread_struct, std::*1::default_delete<std::*1::_thread_struct>>, void (realm::sync::websocket::DefaultSocketProvider::)(), realm::sync::websocket::DefaultSocketProvider_>>(void) + 64
23 libsystem_pthread.dylib 0x30ec _pthread_start + 116
24 libsystem_pthread.dylib 0x172c thread_start + 8

From the older version (realm-dotnet v11.0.0), these reports were coming from about 1.5-2% of the players. Currently, it is much less frequent (around 0.2-0.3%). However, it persists. How can we prevent this?

Unity version: 2021.3.26f1

Repro steps

Unfortunately, we are unable to capture it in our own tests. This error report doesn't occur very often, but it's affecting the smooth operation of our game.

Version

11.3.0

What Atlas Services are you using?

Both Atlas Device Sync and Atlas App Services

What type of application is this?

Unity

Client OS and version

iOS16.6.0

Code snippets

No response

Stacktrace of the exception/crash you're getting

No response

Relevant log output

No response