Keep fields Unity can't serialise out of Unity's serialisation Unity serialises public fields of [Serializable] classes and behaviours, and the 6.7 and CoreCLR branch found these ones, whose types Unity can't serialise (nullables, HashSets, tuples, object), coming up as serialisation issues under CoreCLR. Unity 6.3 already skips them, so marking them [NonSerialized] changes nothing on Mono. Hand-ported from unity_6.7.0's changeset 169906" class="changeset">169906 (ab1e999ad3c, "Fix some more serialisation issues that came up when switching to CoreCLR"), with one difference. 169906" class="changeset">169906 marks the test runner's JSON fields (TestRunner.TestDefinition and TestMethodGroup's TimeoutSeconds, TestListExporter.TestEntry.TimeoutSeconds, TestResultEntry.Parameter) [NonSerialized, JsonProperty], but Json.NET ignores a [NonSerialized] field even with [JsonProperty] (checked with Newtonsoft.Json 13.0.3): test lists would lose their timeouts and results their parameters. Here they become auto-properties instead, which Unity's serialiser skips and Json.NET reads and writes by name, as before; only their position in the written JSON moves after the fields. unity_6.7.0 has the same problem and could take the same fix. Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>