Unity Enter Play Mode Settings: diagnosing stale static state across Play sessions when Reload Domain is disabled

Direct answer

Disable Reload Domain and Reload Scene only when the project either contains no persistent static mutable state and no runtime scene mutations, or when every such state is deterministically reset at the start of each Play session. If static fields, cached singletons, or event subscriptions survive between sessions—or if the open scene is modified at runtime—Play sessions will reflect prior state rather than a clean build.

Likely explanation vs. confirmed behavior

The likely explanation for stale behavior is that the AppDomain persists across Play sessions when Reload Domain is disabled, so static state survives. Confirmed behavior: with Reload Scene disabled, runtime edits to the open scene persist, meaning Awake and Start paths may not execute as they would in a standalone build.

Steps to confirm no leaks

1. Audit static state. List every static field, singleton, and event subscription that can change during Play.
2. Add a reset hook. Decorate a method with [RuntimeInitializeOnLoadMethod(RuntimeInitializeLoadType.SubsystemRegistration)] and use it to null or reset known static state. This hook runs each Play session even when domain reload is disabled, but it does not automatically reset arbitrary static state—you must cover every path.
3. Add a temporary guard. At session start, log or assert if any static value is non-default. Remove the guard once the reset logic is verified.
4. Check scene mutations. Before entering Play, commit or back up the open scene. After exiting Play, inspect the scene in version control or compare it against the backup. Any runtime object moves, spawns, or property edits that remain indicate a leak.
5. Compare against a build. Run a standalone player build and compare its initial state and logs against an Editor Play session with reloads disabled to detect divergence.

Version-sensitive items to verify

Because these options and API members were refined across the 2019.3-era through current LTS and Unity 6 releases, treat any specific default or member name as version-dependent until checked against your Editor's release notes. Confirm the exact RuntimeInitializeLoadType members and their casing for your version. Documented members include AfterAssembliesLoaded, BeforeSplashScreen, BeforeSceneLoad, AfterSceneLoad, and SubsystemRegistration, but availability and spelling have changed across releases. Also confirm the default Enter Play Mode values in Project Settings > Editor; Reload Domain and Reload Scene are typically enabled by default, but defaults and UI labels have been refined over time.

Missing diagnostic

Does the project contain static mutable state or runtime scene edits? If neither exists, disabling reloads is lower risk. If either exists, explicit reset logic is mandatory before disabling.