Repro Steps:
- start new project
- install Alembic package
- drag and drop the "uploads_files_2071884_Leather chair.abc" file in to the project and add it to the scene
- build and run, using Debug build so that you can observe the errors more easily.

The errors:
A scripted object (probably UnityEngine.Formats.Alembic.Importer.AlembicStreamDescriptor?) has a different serialization layout when loading. (Read 76 bytes but expected 212 bytes)
Did you #ifdef UNITY_EDITOR a section of your serialized properties in any of your scripts?
(Filename: C:\buildslave\unity\build\Runtime/Serialize/SerializedFile.cpp Line: 2376)

Does not repro in MacOS, only on Win10, only for x86 builds. x86_64 builds are fine.
Does not repro after rebuilding the library for the project.

Reproduces in: 2020.2.0a19, 2019.4.6f1,2019.4. 5f1 and 2020.1.1f1, 2019.3, 2019.2

Issue reproduces with Alembic Packags and USD package . I tried various versions and it seems like the issue is package-independent. It's something to do with the Editor itself.

Workaround: build for x64 instead of x86