How to reproduce:
1. Open the attached “CrashRepro“ project
2. Open the “Assets/Scenes/GameScene.unity“ Scene
3. Enter Play Mode
4. Move around in the Scene with the “WASD“ keyboard buttons

Reproducible with: 6000.3.0b8, 6000.4.0a4
Couldn’t test with: 6000.0.61f1, 6000.2.10f1 ( Error “The type or namespace name 'LowLevelPhysics2D' does not exist in the namespace 'UnityEngine' “ in the Console)

Reproducible on: macOS Tahoe 26.0.1 (Intel), Windows 10 (by user)
Not reproducible on: No other environment tested

Note: If the line “{{_playerPhysicsBody.transformObject = playerTransform;}}“ is removed in the “Player“ Script, Unity will no longer crash

First few lines of the stack trace:
0x00007FFC2C9F4E44 (Unity) block_merge_next
0x00007FFC2C9F58AD (Unity) tlsf_realloc_align_inplace
0x00007FFC2D7AD4BF (Unity) DynamicHeapAllocator::Reallocate
0x00007FFC2D7ACE60 (Unity) DualThreadAllocator<DynamicHeapAllocator>::Reallocate
0x00007FFC2D7ADB30 (Unity) MemoryManager::Reallocate
0x00007FFC2D7B13BF (Unity) realloc_internal