Reproduction steps:
1. Open the attached "repro_IN-36667CustomEditor.zip" project
2. In the Inspector window click on any GameObject
3. Observe the Console window

Expected result: No errors are displayed and the custom Transform Editor appears
Actual result: "Monoscript is registered as both Editor and Runtime script!" and "Instance of TransformEditor couldn't be created. The script class needs to derive from ScriptableObject and be placed in the Assets/Editor folder." errors displayed and the custom Transform Editor does not appear

Reproducible with: 2022.2.0a3, 2022.2.13f1, 2023.1.0b10, 2023.2.0a9
Not reproducible with: 2020.3.47f1, 2021.3.22f1, 2022.2.0a2

Reproducible on: Windows 10

Note: Reproduction of this issue is inconsistent. Reproducible only the first time, when opening the Unity Editor. Delete the Library folder and try again if the issue is not reproducible. It is also possible that only one error is shown in the Console window and the custom Editor appears.