I got the following error this evening, and something similar happened when I tried to relaunch this client (I didn't cut-n-paste the second error message, but it happened while still checking files). The official client is working.
java.lang.RuntimeException: Delayed error in resource gfx/terobjs/bumlings/apatite0 (v2), from forking source backed by HTTP res source (
https://www.havenandhearth.com/res/)
	at haven.Resource$Pool$Queued.get(Resource.java:456)
	at haven.Resource$Pool$Queued.get(Resource.java:424)
	at haven.Session$CachedRes$Ref.get(Session.java:140)
	at haven.Session$CachedRes$Ref.get(Session.java:133)
	at haven.ResDrawable.<init>(ResDrawable.java:45)
	at haven.OCache.cres(OCache.java:258)
	at haven.OCache.lambda$cres$10(OCache.java:270)
	at haven.OCache$GobInfo.apply(OCache.java:759)
	at haven.Loader.lambda$defer$0(Loader.java:235)
	at haven.Loader$Future.run(Loader.java:71)
	at haven.Loader$Future.access$400(Loader.java:42)
	at haven.Loader.loop(Loader.java:197)
	at java.lang.Thread.run(Thread.java:748)
Caused by: haven.Resource$LoadException: Load error in resource gfx/terobjs/bumlings/apatite0(v2), from forking source backed by HTTP res source (
https://www.havenandhearth.com/res/)
	at haven.Resource$Pool.handle(Resource.java:517)
	at haven.Resource$Pool.access$1200(Resource.java:401)
	at haven.Resource$Pool$Loader.run(Resource.java:653)
	... 1 more
	Suppressed: haven.Resource$LoadException: Load error in resource gfx/terobjs/bumlings/apatite0(v2), from cache source backed by HashDirCache(
http://game.havenandhearth.com/render/)
		... 4 more
		Suppressed: haven.Resource$LoadException: Load error in resource gfx/terobjs/bumlings/apatite0(v2), from local res source (res-preload)
			... 4 more
			Suppressed: haven.Resource$LoadException: Load error in resource gfx/terobjs/bumlings/apatite0(v2), from 'custom' jar source
				... 4 more
				Suppressed: haven.Resource$LoadException: Load error in resource gfx/terobjs/bumlings/apatite0(v2), from local res source (res)
					... 4 more
					Suppressed: haven.Resource$LoadException: Load error in resource gfx/terobjs/bumlings/apatite0(v2), from filesystem res source (/private/var/folders/zk/926c34c13hg6y_y5gyvp7hy40000gn/T/hsperfdata_arlie/res)
						... 4 more
					Caused by: java.io.FileNotFoundException: gfx/terobjs/bumlings/apatite0
						at haven.Resource$FileSource.get(Resource.java:269)
						at haven.Resource$Pool.handle(Resource.java:501)
						... 3 more
					Caused by: java.nio.file.NoSuchFileException: /private/var/folders/zk/926c34c13hg6y_y5gyvp7hy40000gn/T/hsperfdata_arlie/res/gfx/terobjs/bumlings/apatite0.res
						at sun.nio.fs.UnixException.translateToIOException(UnixException.java:86)
						at sun.nio.fs.UnixException.rethrowAsIOException(UnixException.java:102)
						at sun.nio.fs.UnixException.rethrowAsIOException(UnixException.java:107)
						at sun.nio.fs.UnixFileSystemProvider.newByteChannel(UnixFileSystemProvider.java:214)
						at java.nio.file.Files.newByteChannel(Files.java:361)
						at java.nio.file.Files.newByteChannel(Files.java:407)
						at java.nio.file.spi.FileSystemProvider.newInputStream(FileSystemProvider.java:384)
						at java.nio.file.Files.newInputStream(Files.java:152)
						at haven.Resource$FileSource.get(Resource.java:267)
						... 4 more
				Caused by: java.io.FileNotFoundException: Could not find resource locally: /res/gfx/terobjs/bumlings/apatite0.res
					at haven.Resource$JarSource.get(Resource.java:289)
					at haven.Resource$Pool.handle(Resource.java:501)
					... 3 more
			Caused by: java.io.FileNotFoundException: Could not find resource locally: /customized-remote/gfx/terobjs/bumlings/apatite0.res
				at haven.Resource$JarSource.get(Resource.java:289)
				at haven.Resource$CustomizedJarSource.get(Resource.java:307)
				at haven.Resource$Pool.handle(Resource.java:501)
				... 3 more
		Caused by: java.io.FileNotFoundException: Could not find resource locally: /res-preload/gfx/terobjs/bumlings/apatite0.res
			at haven.Resource$JarSource.get(Resource.java:289)
			at haven.Resource$Pool.handle(Resource.java:501)
			... 3 more
	Caused by: java.io.FileNotFoundException: res/gfx/terobjs/bumlings/apatite0
		at haven.HashDirCache.fetch(HashDirCache.java:389)
		at haven.Resource$CacheSource.get(Resource.java:232)
		at haven.Resource$Pool.handle(Resource.java:501)
		... 3 more
Caused by: haven.StreamMessage$IOError: java.io.IOException: already retried 7 times
	at haven.StreamMessage.underflow(StreamMessage.java:71)
	at haven.Message.rensure(Message.java:98)
	at haven.Message.bytes(Message.java:171)
	at haven.Resource.load(Resource.java:1626)
	at haven.Resource.access$700(Resource.java:41)
	at haven.Resource$Pool.handle(Resource.java:505)
	... 3 more
Caused by: java.io.IOException: already retried 7 times
	at haven.RetryingInputStream.retry(RetryingInputStream.java:54)
	at haven.RetryingInputStream.get(RetryingInputStream.java:70)
	at haven.RetryingInputStream.read(RetryingInputStream.java:111)
	at haven.StreamTee.read(StreamTee.java:87)
	at haven.StreamMessage.underflow(StreamMessage.java:68)
	... 8 more
Caused by: javax.net.ssl.SSLHandshakeException: sun.security.validator.ValidatorException: PKIX path building failed: sun.security.provider.certpath.SunCertPathBuilderException: unable to find valid certification path to requested target
	at sun.security.ssl.Alert.createSSLException(Alert.java:131)
	at sun.security.ssl.TransportContext.fatal(TransportContext.java:370)
	at sun.security.ssl.TransportContext.fatal(TransportContext.java:313)
	at sun.security.ssl.TransportContext.fatal(TransportContext.java:308)
	at sun.security.ssl.CertificateMessage$T12CertificateConsumer.checkServerCerts(CertificateMessage.java:652)
	at sun.security.ssl.CertificateMessage$T12CertificateConsumer.onCertificate(CertificateMessage.java:471)
	at sun.security.ssl.CertificateMessage$T12CertificateConsumer.consume(CertificateMessage.java:367)
	at sun.security.ssl.SSLHandshake.consume(SSLHandshake.java:376)
	at sun.security.ssl.HandshakeContext.dispatch(HandshakeContext.java:479)
	at sun.security.ssl.HandshakeContext.dispatch(HandshakeContext.java:457)
	at sun.security.ssl.TransportContext.dispatch(TransportContext.java:200)
	at sun.security.ssl.SSLTransport.decode(SSLTransport.java:154)
	at sun.security.ssl.SSLSocketImpl.decode(SSLSocketImpl.java:1290)
	at sun.security.ssl.SSLSocketImpl.readHandshakeRecord(SSLSocketImpl.java:1199)
	at sun.security.ssl.SSLSocketImpl.startHandshake(SSLSocketImpl.java:401)
	at sun.security.ssl.SSLSocketImpl.startHandshake(SSLSocketImpl.java:373)
	at sun.net.www.protocol.https.HttpsClient.afterConnect(HttpsClient.java:587)
	at sun.net.www.protocol.https.AbstractDelegateHttpsURLConnection.connect(AbstractDelegateHttpsURLConnection.java:197)
	at sun.net.www.protocol.http.HttpURLConnection.getInputStream0(HttpURLConnection.java:1584)
	at sun.net.www.protocol.http.HttpURLConnection.getInputStream(HttpURLConnection.java:1512)
	at sun.net.www.protocol.https.HttpsURLConnectionImpl.getInputStream(HttpsURLConnectionImpl.java:268)
	at haven.Resource$HttpSource$1.create(Resource.java:363)
	at haven.RetryingInputStream.create(RetryingInputStream.java:44)
	at haven.RetryingInputStream.get(RetryingInputStream.java:76)
	... 11 more
Caused by: sun.security.validator.ValidatorException: PKIX path building failed: sun.security.provider.certpath.SunCertPathBuilderException: unable to find valid certification path to requested target
	at sun.security.validator.PKIXValidator.doBuild(PKIXValidator.java:439)
	at sun.security.validator.PKIXValidator.engineValidate(PKIXValidator.java:306)
	at sun.security.validator.Validator.validate(Validator.java:271)
	at sun.security.ssl.X509TrustManagerImpl.validate(X509TrustManagerImpl.java:312)
	at sun.security.ssl.X509TrustManagerImpl.checkTrusted(X509TrustManagerImpl.java:221)
	at sun.security.ssl.X509TrustManagerImpl.checkServerTrusted(X509TrustManagerImpl.java:128)
	at sun.security.ssl.CertificateMessage$T12CertificateConsumer.checkServerCerts(CertificateMessage.java:636)
	... 30 more
Caused by: sun.security.provider.certpath.SunCertPathBuilderException: unable to find valid certification path to requested target
	at sun.security.provider.certpath.SunCertPathBuilder.build(SunCertPathBuilder.java:141)
	at sun.security.provider.certpath.SunCertPathBuilder.engineBuild(SunCertPathBuilder.java:126)
	at java.security.cert.CertPathBuilder.build(CertPathBuilder.java:280)
	at sun.security.validator.PKIXValidator.doBuild(PKIXValidator.java:434)
	... 36 more
I'm on MacOS 12.0.1 which may be relevant. They have issues of their own with certificates.