Steps to reproduce the IPC Exception:
1. Open the attached project "project.zip"
2. Build for Windows using the Build Profiles, or you can also click on File > XVR Build > OS Debug and this will also trigger the build process (reproduces with both)
3. If the build completes successfully, close the Editor, delete the Library folder, start from step 1 again. This will force recompile all the shaders

Actual result: the build will fail with an "Internal error communicating with the shader compiler process" error
Expected results: the build always completes successfully

Steps to reproduce the crash:
1. Configure the following environment variables on the PC:
UNITY_SHADER_COMPILER_CONNECT_TIMEOUT_SECONDS = 30, UNITY_SHADER_COMPILER_TASK_TIMEOUT_MINUTES = 30, UNITY_SHADER_COMPILER_RETRY_COUNT 3
2. You might need to restart your PC for the changes to take effect
3. Follow the same instructions as for the IPC exception (i.e. make a clean build of the project)
4. Instead of failing with an IPC Exception, it will crash

Reproducible with according to the customer: 6000.3.0a2, 6000.3.14f1, 6000.6.0a5
Not reproducible with according to the customer: 6000.2.0f1
Could not locally test on 6000.0.75f1, 6000.3.16f1, 6000.4.8f1, 6000.5.0b9, 6000.6.0a5 due to missing hardware

Reproduces on the following:
AMD Ryzen 9 9950X3D 16-Core CPU and NVIDIA GeForce RTX 5060
AMD Ryzen 9 9950X3D 16-Core CPU with an AMD Radeon(™) Graphics card and an NVIDIA GeForce RTX 5070

It does not reproduce on the following :
Intel(R) Xeon(R) W-2295, Nvidia GeForce RTX 3090
Intel(R) Xeon(R) W-2145 CPU, Nvidia GeForce GTX 1070
Intel(R) Core(™) Ultra 9 285 K, Nvidia GeForce RTX 5080
Intel® Core™ Ultra 9 285K (24 Core), AMD Radeon RX 6900 XT
Macbook Pro Apple M1 Max, macOS Sequoia 15.7.15

Notes:
-Both happen quite often and at least once every 10 builds, but usually more (usually once every other build, sometimes repeatedly in a few consecutive builds).
-Full error:
Shader compiler: Compile XVR/Standard - Universal Forward, Fragment Program: Internal error communicating with the shader compiler process. Please report a bug including this shader and the editor log. Error code 0x80000004 (Not connected).
-If the UNITY_SHADER_COMPILER_RETRY_COUNT environment variable is added to try to prevent the IPC Exceptions, the Editor will instead crash with the following callstack:
0x00007FFF5425D0E0 (Unity) Baselib_ReentrantLock_Release
0x00007FFF5608A22B (Unity) ShaderCompilerCompileSnippet
0x00007FFF5529BF6D (Unity) CompileShaderSnippet
0x00007FFF5529E68B (Unity) GetSerializedSubProgramForShaderSnippet
0x00007FFF572A2360 (Unity) ShaderCompilation::CompileVariantJob
0x00007FFF54FCC697 (Unity) ujob_execute_job
0x00007FFF54FCB8EB (Unity) lane_guts
0x00007FFF54FCEFF9 (Unity) worker_thread_routine
0x00007FFF5616F450 (Unity) Thread::RunThreadWrapper
0x00007FF823FCE8D7 (KERNEL32) BaseThreadInitThunk
0x00007FF825BEC3FC (ntdll) RtlUserThreadStart