на следующий день всё заработало корректно.

org.springframework.web.reactive.function.client.WebClientRequestException: Этот хост неизвестен (api.faforever.com); nested exception is java.net.UnknownHostException: Этот хост неизвестен (api.faforever.com)
at org.springframework.web.reactive.function.client.ExchangeFunctions$DefaultExchangeFunction.lambda$wrapException$9(ExchangeFunctions.java:141)
Suppressed: The stacktrace has been enhanced by Reactor, refer to additional information below:
Error has been observed at the following site(s):
*__checkpoint ⇢ Request to GET https://api.faforever.com/me [DefaultWebClient]
Original Stack Trace:
at org.springframework.web.reactive.function.client.ExchangeFunctions$DefaultExchangeFunction.lambda$wrapException$9(ExchangeFunctions.java:141)
at reactor.core.publisher.MonoErrorSupplied.subscribe(MonoErrorSupplied.java:55)
at reactor.core.publisher.Mono.subscribe(Mono.java:4397)
at reactor.core.publisher.FluxOnErrorResume$ResumeSubscriber.onError(FluxOnErrorResume.java:103)
at reactor.core.publisher.FluxPeek$PeekSubscriber.onError(FluxPeek.java:222)
at reactor.core.publisher.FluxPeek$PeekSubscriber.onError(FluxPeek.java:222)
at reactor.core.publisher.FluxPeek$PeekSubscriber.onError(FluxPeek.java:222)
at reactor.core.publisher.MonoNext$NextSubscriber.onError(MonoNext.java:93)
at reactor.core.publisher.MonoFlatMapMany$FlatMapManyMain.onError(MonoFlatMapMany.java:204)
at reactor.core.publisher.SerializedSubscriber.onError(SerializedSubscriber.java:124)
at reactor.core.publisher.FluxRetryWhen$RetryWhenMainSubscriber.whenError(FluxRetryWhen.java:225)
at reactor.core.publisher.FluxRetryWhen$RetryWhenOtherSubscriber.onError(FluxRetryWhen.java:274)
at reactor.core.publisher.FluxConcatMap$ConcatMapImmediate.drain(FluxConcatMap.java:415)
at reactor.core.publisher.FluxConcatMap$ConcatMapImmediate.onNext(FluxConcatMap.java:251)
at reactor.core.publisher.EmitterProcessor.drain(EmitterProcessor.java:537)
at reactor.core.publisher.EmitterProcessor.tryEmitNext(EmitterProcessor.java:343)
at reactor.core.publisher.SinkManySerialized.tryEmitNext(SinkManySerialized.java:100)
at reactor.core.publisher.InternalManySink.emitNext(InternalManySink.java:27)
at reactor.core.publisher.FluxRetryWhen$RetryWhenMainSubscriber.onError(FluxRetryWhen.java:190)
at reactor.core.publisher.MonoCreate$DefaultMonoSink.error(MonoCreate.java:201)
at reactor.netty.http.client.HttpClientConnect$MonoHttpConnect$ClientTransportSubscriber.onError(HttpClientConnect.java:308)
at reactor.core.publisher.MonoCreate$DefaultMonoSink.error(MonoCreate.java:201)
at reactor.netty.resources.NewConnectionProvider$DisposableConnect.onError(NewConnectionProvider.java:140)
at reactor.core.publisher.MonoFlatMap$FlatMapMain.secondError(MonoFlatMap.java:192)
at reactor.core.publisher.MonoFlatMap$FlatMapInner.onError(MonoFlatMap.java:259)
at reactor.core.publisher.FluxOnErrorResume$ResumeSubscriber.onError(FluxOnErrorResume.java:106)
at reactor.core.publisher.Operators.error(Operators.java:198)
at reactor.core.publisher.MonoError.subscribe(MonoError.java:53)
at reactor.core.publisher.Mono.subscribe(Mono.java:4397)
at reactor.core.publisher.FluxOnErrorResume$ResumeSubscriber.onError(FluxOnErrorResume.java:103)
at reactor.core.publisher.Operators.error(Operators.java:198)
at reactor.core.publisher.MonoError.subscribe(MonoError.java:53)
at reactor.core.publisher.InternalMonoOperator.subscribe(InternalMonoOperator.java:64)
at reactor.core.publisher.MonoFlatMap$FlatMapMain.onNext(MonoFlatMap.java:157)
at reactor.netty.transport.TransportConnector$MonoChannelPromise._subscribe(TransportConnector.java:596)
at reactor.netty.transport.TransportConnector$MonoChannelPromise.lambda$subscribe$0(TransportConnector.java:516)
at io.netty.util.concurrent.AbstractEventExecutor.runTask(AbstractEventExecutor.java:174)
at io.netty.util.concurrent.AbstractEventExecutor.safeExecute(AbstractEventExecutor.java:167)
at io.netty.util.concurrent.SingleThreadEventExecutor.runAllTasks(SingleThreadEventExecutor.java:470)
at io.netty.channel.nio.NioEventLoop.run(NioEventLoop.java:503)
at io.netty.util.concurrent.SingleThreadEventExecutor$4.run(SingleThreadEventExecutor.java:997)
at io.netty.util.internal.ThreadExecutorMap$2.run(ThreadExecutorMap.java:74)
at io.netty.util.concurrent.FastThreadLocalRunnable.run(FastThreadLocalRunnable.java:30)
at java.base/java.lang.Thread.run(Thread.java:833)
Caused by: java.net.UnknownHostException: Этот хост неизвестен (api.faforever.com)
at java.base/java.net.Inet4AddressImpl.lookupAllHostAddr(Native Method)
at java.base/java.net.InetAddress$PlatformNameService.lookupAllHostAddr(InetAddress.java:933)
at java.base/java.net.InetAddress.getAddressesFromNameService(InetAddress.java:1519)
at java.base/java.net.InetAddress$NameServiceAddresses.get(InetAddress.java:852)
at java.base/java.net.InetAddress.getAllByName0(InetAddress.java:1509)
at java.base/java.net.InetAddress.getAllByName(InetAddress.java:1367)
at java.base/java.net.InetAddress.getAllByName(InetAddress.java:1301)
at io.netty.util.internal.SocketUtils$9.run(SocketUtils.java:169)
at io.netty.util.internal.SocketUtils$9.run(SocketUtils.java:166)
at java.base/java.security.AccessController.doPrivileged(AccessController.java:569)
at io.netty.util.internal.SocketUtils.allAddressesByName(SocketUtils.java:166)
at io.netty.resolver.DefaultNameResolver.doResolveAll(DefaultNameResolver.java:50)
at io.netty.resolver.SimpleNameResolver.resolveAll(SimpleNameResolver.java:79)
at io.netty.resolver.SimpleNameResolver.resolveAll(SimpleNameResolver.java:71)
at io.netty.resolver.InetSocketAddressResolver.doResolveAll(InetSocketAddressResolver.java:73)
at io.netty.resolver.InetSocketAddressResolver.doResolveAll(InetSocketAddressResolver.java:31)
at io.netty.resolver.AbstractAddressResolver.resolveAll(AbstractAddressResolver.java:158)
at reactor.netty.transport.TransportConnector.doResolveAndConnect(TransportConnector.java:300)
at reactor.netty.transport.TransportConnector.lambda$connect$6(TransportConnector.java:127)
at reactor.core.publisher.MonoFlatMap$FlatMapMain.onNext(MonoFlatMap.java:125)
at reactor.netty.transport.TransportConnector$MonoChannelPromise._subscribe(TransportConnector.java:596)
at reactor.netty.transport.TransportConnector$MonoChannelPromise.lambda$subscribe$0(TransportConnector.java:516)
at io.netty.util.concurrent.AbstractEventExecutor.runTask(AbstractEventExecutor.java:174)
at io.netty.util.concurrent.AbstractEventExecutor.safeExecute(AbstractEventExecutor.java:167)
at io.netty.util.concurrent.SingleThreadEventExecutor.runAllTasks(SingleThreadEventExecutor.java:470)
at io.netty.channel.nio.NioEventLoop.run(NioEventLoop.java:503)
at io.netty.util.concurrent.SingleThreadEventExecutor$4.run(SingleThreadEventExecutor.java:997)
at io.netty.util.internal.ThreadExecutorMap$2.run(ThreadExecutorMap.java:74)
at io.netty.util.concurrent.FastThreadLocalRunnable.run(FastThreadLocalRunnable.java:30)
at java.base/java.lang.Thread.run(Thread.java:833)