How to reproduce:
1. Open attached project "MarshallOffsetOfIssue.zip" with IL2CPP Editor
2. Open Scene "SampleScene"
3. Enter Play mode (observe the OriginalVector3 and offsets)
4. Build and Run with IL2CPP (observe the OriginalVector3 and offsets)

Expected result: Editor and Build has the same results (1.1, 2.2, 3.3)
"idOffset: 0; worldPositionOffset: 4; typeOffset: 16; OriginalVector (1.1, 2.2, 3.3); id: 123; Vector (1.1, 2.2, 3.3); type: 4"

Actual result: On Build the offset vector is incorrect
"idOffset: 0; worldPositionOffset: 12; typeOffset: 24; OriginalVector (1.1, 2.2, 3.3); id: 123; Vector (3.3, 5.605194E-45, 6.869364E-36); type: -1826805822"

Reproducible with: 2018.4.13f1, 2019.2.14f1, 2019.3.0f1, 2020.1.0a15
Could not test with: 2017.4 (IL2CPP was not yet released)