NuGet Proxy does not work with some third-party V3 repositories

C:\Program Files\dotnet\sdk\3.1.302\NuGet.targets(128,5): error : Unable to load the service index for source http://localhsot:8081/repository/nuget-test-v3/index.json. [D:\src\rdn\Reserve.Locker.ForceConnect\ForceConnect.sln] rve.Locker.ForceConnect\ForceConnect.sln]
C:\Program Files\dotnet\sdk\3.1.302\NuGet.targets(128,5): error : Response status code does not indicate success: 404 (Not Found). [D:\src\rdn\Reserve.Locker.ForceConnect\ForceConnect.sln]

2020-09-18 18:04:09,926-0400 DEBUG [qtp1448435497-12022]  *UNKNOWN org.sonatype.nexus.httpclient.outbound - https://nuget.hangfire.io/nuget/hangfire-ace/v3/index.json/ > GET /nuget/hangfire-ace/v3/index.json/ HTTP/1.1^M
2020-09-18 18:04:09,926-0400 DEBUG [qtp1448435497-12022]  *UNKNOWN org.sonatype.nexus.internal.httpclient.SharedHttpClientConnectionManager - Connection request: [route: {s}->https://nuget.hangfire.io:443][total kept alive: 0; route allocated: 0 of 20; total allocated: 0 of 200]^M
2020-09-18 18:04:09,926-0400 DEBUG [qtp1448435497-12022]  *UNKNOWN org.sonatype.nexus.internal.httpclient.SharedHttpClientConnectionManager - Connection leased: [id: 3717][route: {s}->https://nuget.hangfire.io:443][total kept alive: 0; route allocated: 1 of 20; total allocated: 1 of 200]^M
2020-09-18 18:04:10,004-0400 DEBUG [qtp1448435497-12022]  *UNKNOWN org.sonatype.nexus.httpclient.outbound - https://nuget.hangfire.io/nuget/hangfire-ace/v3/index.json/ < HTTP/1.1 404 Not Found @ 82.02 ms^M
... (snip) ...
2020-09-18 17:55:06,822-0400 WARN  [qtp1448435497-11993]  *UNKNOWN org.sonatype.nexus.repository.httpbridge.internal.ViewServlet - Failure servicing: GET /repository/nuget-test-v3/v3/content/hangfire.throttling/index.json^M
java.lang.RuntimeException: Service Index unavailable^M
        at com.sonatype.nexus.repository.nuget.internal.v3.NugetV3ProxyFacetImpl.getServiceIndex(NugetV3ProxyFacetImpl.java:109)^M
        at com.sonatype.nexus.repository.nuget.internal.v3.NugetV3GroupHelper.getPaths(NugetV3GroupHelper.java:89)^M
        at com.sonatype.nexus.repository.nuget.internal.v3.NugetV3GroupHelper.lambda$2(NugetV3GroupHelper.java:83)^M
        at java.util.stream.ReferencePipeline$3$1.accept(ReferencePipeline.java:193)^M
        at java.util.ArrayList$ArrayListSpliterator.forEachRemaining(ArrayList.java:1382)^M
        at java.util.stream.AbstractPipeline.copyInto(AbstractPipeline.java:482)^M
        at java.util.stream.AbstractPipeline.wrapAndCopyInto(AbstractPipeline.java:472)^M
        at java.util.stream.ReduceOps$ReduceOp.evaluateSequential(ReduceOps.java:708)^M
        at java.util.stream.AbstractPipeline.evaluate(AbstractPipeline.java:234)^M
        at java.util.stream.ReferencePipeline.collect(ReferencePipeline.java:566)^M
        ...