Reproduction steps:
1. Open the attached “repro” project
2. Click File > Build Setttings > Build And Run
3. In Player, click “Load” on all Sections
4. In Player, click “Unload” immediately as it appears
5. Repeat from 3rd step

Expected Results: Subscenes are loaded and unloaded without any issues
Actual Results: Player crashes

Reproduced with: 2022.3.21f1, 2022.3.22f1, 2023.2.15f1
Not reproduced with: 2022.3.20f1, 6000.0.0b12 (0ac662189661)
Couldn’t test with: 2021.3.35f1 (Project uses DOTS, so it can’t be downgraded)

Reproduced on: Ubuntu 22.04, Windows 10
Not reproduced on: No other environment tested

First lines of the Player stack trace:
#5 0x007e717af382d5 in BatchRendererGroup_UnregisterMaterial_m1A912834A8206072C163C5640C6A1448BC27CF24
#6 0x007e717aa25f9e in RegisterMaterialsAndMeshesSystem_UnregisterMaterialsMeshes_m96BDD648CF34533DF24183797EFFDDB9FAD0EECE
#7 0x007e717aa259e2 in RegisterMaterialsAndMeshesSystem_RegisterMaterialsAndMeshes_m0BBDF35C823098579E5012C5C2B8EBCAD4A477A3
#8 0x007e717aa24c3c in RegisterMaterialsAndMeshesSystem_OnUpdate_m95C7FBEFFC769D813A8A4B2D7B9CD76F9492E019
#9 0x007e717abcee76 in SystemBase_Update_m795994EE60C054DFA78C313A60ED025B2668C9B4

Notes:

• Reproduces with both Mono and IL2CPP builds
• Reproduces on 2022.3.21f1 and does not reproduce on 2022.3.20f1 with the same Entities version (10.0.10), so this is not Entities fault
• Possibly introduced by UUM-54573 (https://issuetracker.unity3d.com/product/unity/issues/guid/UUM-54573)