static func getContestLastSyncVersion(contestId: String) -> Single<Int> {
        return Single.deferred {
            let realm = try Realm.tryCreate()
            // next line will crash on very rare occasions
            let items = realm.objects(CacheContest.self).filter("id == %@", contestId)
            return Single.just(items.first?.contestMessages.max(ofProperty: "syncVersion") ?? 0)
        }
    }

MAIN THREAD - CRASHED
libsystem_platform.dylib   _platform_memcmp
Realm    realm::Group::do_get_table(realm::StringData, bool (*)(realm::Spec const&))
Realm    realm::ObjectStore::table_for_object_type(realm::Group&, realm::StringData) group.hpp:939
Realm    (anonymous namespace)::get_table(realm::Group&, RLMObjectSchema*) RLMQueryUtil.mm:206
Realm    RLMPredicateToQuery(NSPredicate*, RLMObjectSchema*, RLMSchema*, realm::Group&) RLMQueryUtil.mm:1474
Realm    -[RLMResults objectsWithPredicate:] RLMResults.mm:361
RealmSwift    function signature specialization <Arg[0] = Exploded> of RealmSwift.Results.filter(Swift.String, Any...) -> RealmSwift.Results<A> Results.swift:211
Hanako    closure #1 () throws -> RxSwift.PrimitiveSequence<RxSwift.SingleTrait, Swift.Int> in static Hanako.ContestCacheImpl.getContestLastSyncVersion(contestId: Swift.String) -> RxSwift.PrimitiveSequence<RxSwift.SingleTrait, Swift.Int> ContestCacheImpl.swift:220
Hanako    partial apply forwarder for closure #1 () throws -> RxSwift.PrimitiveSequence<RxSwift.SingleTrait, Swift.Int> in static Hanako.ContestCacheImpl.getContestLastSyncVersion(contestId: Swift.String) -> RxSwift.PrimitiveSequence<RxSwift.SingleTrait, Swift.Int> <compiler-generated>:0
RxSwift   partial apply forwarder for closure #1 () throws -> RxSwift.Observable<B> in static RxSwift.PrimitiveSequence.deferred(() throws -> RxSwift.PrimitiveSequence<A, B>) -> RxSwift.PrimitiveSequence<A, B> PrimitiveSequence.swift:69
RxSwift   partial apply forwarder for reabstraction thunk helper <A where A: RxSwift.ObservableType> from @escaping @callee_guaranteed () -> (@owned RxSwift.Observable<A.E>, @error @owned Swift.Error) to @escaping @callee_guaranteed () -> (@out RxSwift.Observable<A.E>, @error @owned Swift.Error) <compiler-generated>:0
RxSwift   RxSwift.(DeferredSink in _9A640CB28D6420293D75F113534DFAC6).run() -> RxSwift.Disposable Deferred.swift:36
RxSwift   RxSwift.(Deferred in _9A640CB28D6420293D75F113534DFAC6).run<A where A1: RxSwift.ObserverType, A.E == A1.E>(_: A1, cancel: RxSwift.Cancelable) -> (sink: RxSwift.Disposable, subscription: RxSwift.Disposable) Deferred.swift:71
RxSwift   RxSwift.Producer.subscribe<A where A == A1.E, A1: RxSwift.ObserverType>(A1) -> RxSwift.Disposable Producer.swift:18
RxSwift   RxSwift.(MergeSink in _DDEA0423368B3B462AE46699A4D080E1).run(RxSwift.Observable<A>) -> RxSwift.Disposable Merge.swift:507
RxSwift   merged RxSwift.(FlatMap in _DDEA0423368B3B462AE46699A4D080E1).run<A where A1: RxSwift.ObserverType, B.E == A1.E>(_: A1, cancel: RxSwift.Cancelable) -> (sink: RxSwift.Disposable, subscription: RxSwift.Disposable)
RxSwift   closure #1 (()) -> RxSwift.Disposable in RxSwift.Producer.subscribe<A where A == A1.E, A1: RxSwift.ObserverType>(A1) -> RxSwift.Disposable Producer.swift:26
RxSwift   function signature specialization <Arg[2] = [Closure Propagated : reabstraction thunk helper from @escaping @callee_guaranteed () -> (@out RxSwift.Disposable) to @escaping @callee_guaranteed (@in_guaranteed ()) -> (@out RxSwift.Disposable), Argument Types : [@escaping @callee_guaranteed () -> (@out RxSwift.Disposable)]> of generic specialization <()> of RxSwift.CurrentThreadScheduler.schedule<A>(_: A, action: (A) -> RxSwift.Disposable) -> RxSwift.Disposable <compiler-generated>:0
RxSwift   RxSwift.Producer.subscribe<A where A == A1.E, A1: RxSwift.ObserverType>(A1) -> RxSwift.Disposable Producer.swift:24
RxSwift   (extension in RxSwift):   RxSwift.ObservableType.subscribe((RxSwift.Event<A.E>) -> ()) -> RxSwift.Disposable ObservableType+Extensions.swift:25
Hanako    closure #1 (RxSwift.Event<Swift.Int>) -> () in Hanako.ContestChatViewModel.refreshMessages(tableView: __C.UITableView?) -> () ContestChatViewModel.swift:133
Hanako    reabstraction thunk helper from @escaping @callee_guaranteed (@guaranteed RxSwift.Event<Swift.Int>) -> () to @escaping @callee_guaranteed (@in_guaranteed RxSwift.Event<Swift.Int>) -> () <compiler-generated>:0
RxSwift   partial apply forwarder for closure #1 (RxSwift.Event<A.E>) -> () in (extension in RxSwift):RxSwift.ObservableType.subscribe((RxSwift.Event<A.E>) -> ()) -> RxSwift.Disposable ObservableType+Extensions.swift:23
RxSwift   RxSwift.AnonymousObserver.onCore(RxSwift.Event<A>) -> () AnonymousObserver.swift:24
RxSwift   RxSwift.ObserverBase.on(RxSwift.Event<A>) -> () ObserverBase.swift:18
RxSwift   protocol witness for RxSwift.ObserverType.on(RxSwift.Event<A.E>) -> () in conformance RxSwift.ObserverBase<A> : RxSwift.ObserverType in RxSwift <compiler-generated>:0
RxSwift   RxSwift.Sink.forwardOn(RxSwift.Event<A.E>) -> () Sink.swift:34
RxSwift   closure #1 (A.E) -> A.E in RxSwift.(TimerSink in _92B4E76F25CED73665C45EB7986E9847).run() -> RxSwift.Disposable Timer.swift:66
RxSwift   closure #2 () -> () in RxSwift.DispatchQueueConfiguration.schedulePeriodic<A>(_: A, startAfter: Swift.Double, period: Swift.Double, action: (A) -> A) -> RxSwift.Disposable DispatchQueueConfiguration.swift:98
RxSwift   reabstraction thunk helper from @escaping @callee_guaranteed () -> () to @escaping @callee_unowned @convention(block) () -> () <compiler-generated>:0

static func getDate(_ key: String, defValue: Date = Date()) -> Date {
  guard
	let realm = try? Realm.tryCreate(),
        // next line will also crash on very rare occasions
	let item = realm.object(ofType: CacheDateValue.self, forPrimaryKey: key) else {
		return defValue
	}
	return item.value
}

        let timer = DispatchSource.makeTimerSource(queue: self.queue)
        timer.schedule(deadline: initial, repeating: dispatchInterval(period), leeway: self.leeway)
        timer.setEventHandler(handler: {
            if cancelTimer.isDisposed {
                return
            }
            timerState = action(timerState)
        })

Installing Realm (3.21.0)
Installing RealmSwift (3.21.0)
Installing RxRealm (0.7.6)
Installing RxSwift (4.5.0)