AuthenticationFailure thrown when accessing bucket while combination testing

Combination testing fails for every request in Jenkins:

X Couchbase.IntegrationTests.ExistsTests.Exists_returns_cas [12s 565ms]
Error Message:
Couchbase.AuthenticationFailureException : Exception of type 'Couchbase.AuthenticationFailureException' was thrown.
Stack Trace:
at Couchbase.Core.ClusterContext.GetOrCreateBucketAsync(String name) in /data/workspace/dotnet-sdk/couchbase-net-client-scripted-build-pipeline/couchbase-net-client/src/Couchbase/Core/ClusterContext.cs:line 272
at Couchbase.Cluster.BucketAsync(String name) in /data/workspace/dotnet-sdk/couchbase-net-client-scripted-build-pipeline/couchbase-net-client/src/Couchbase/Cluster.cs:line 124
at Couchbase.IntegrationTests.Fixtures.ClusterFixture.GetDefaultBucket() in /data/workspace/dotnet-sdk/couchbase-net-client-scripted-build-pipeline/couchbase-net-client/tests/Couchbase.IntegrationTests/Fixtures/ClusterFixture.cs:line 29
at Couchbase.IntegrationTests.Fixtures.ClusterFixture.GetDefaultCollection() in /data/workspace/dotnet-sdk/couchbase-net-client-scripted-build-pipeline/couchbase-net-client/tests/Couchbase.IntegrationTests/Fixtures/ClusterFixture.cs:line 34
at Couchbase.IntegrationTests.ExistsTests.Exists_returns_cas() in /data/workspace/dotnet-sdk/couchbase-net-client-scripted-build-pipeline/couchbase-net-client/tests/Couchbase.IntegrationTests/ExistsTests.cs:line 44

This likely an environment or script issue, although the script looks correct: http://sdk.jenkins.couchbase.com/job/dotnet-sdk/job/couchbase-net-client-scripted-build-pipeline

Will need to add additional logging output to determine what exactly is going on.