Build is failing to run tests on multiple libraries

We are running tests via “dotnet test”, and our TeamCity builds haven't been running all of our tests. This changed recently, and I don't see any TC setting changes nor code changes that would impact this. We are able to re-run the same build and sometimes have it succeed, so it seems somewhat random. (We have two test agents on separate servers, but that doesn't seem to be a factor either.)

Here's a successful log:

[08:09:21] :         [dotnet test] Total tests: 601

[08:09:21] :         [dotnet test]      Passed: 574

[08:09:21] :         [dotnet test]      Failed: 3

[08:09:21] :         [dotnet test]     Skipped: 24

[08:09:21]W:         [dotnet test] Test Run Failed.

[08:09:21] :         [dotnet test]  Total time: 12.6113 Minutes

[08:09:21]W:         [dotnet test] Process exited with code 1

[08:09:21]W:     [Step 1/2] Process finished with positive exit code 1 (some tests have failed). Reporting step success as all the tests have run.

[08:09:21]E:     [Step 1/2] dotnet test (53m:37s)

And here's a failed version:

[08:28:40] :         [dotnet test] Total tests: 601

[08:28:40] :         [dotnet test]      Passed: 575

[08:28:40] :         [dotnet test]      Failed: 2

[08:28:40] :         [dotnet test]     Skipped: 24

[08:28:40]W:         [dotnet test] Test Run Failed.

[08:28:40] :         [dotnet test]  Total time: 11.9931 Minutes

[08:28:40]W:         [dotnet test] Process exited with code 1

[08:28:40]E:     [Step 1/2] Process exited with code 1 (Step: NUnit Tests (.NET))

[08:28:40] :     [Step 1/2] Waiting for 6 service processes to complete

Both times it exited with code 1, but in one case it was a warning and it started tests on the next library, but in the failed case it was an error and aborted further test runs.