Known issues

• When Bidirectional cannot run, the render uses Photon Caustics instead and tells you why: with a shadow catcher, a rolling shutter, an unsupported custom-camera setup, depth of field or spherical stereo on a panoramic camera, or OSL materials on a GPU. With motion blur, only caustics seen directly keep the Bidirectional benefit.
• OptiX. The first render that uses Photon Caustics, Photon Training or the Bidirectional/VCM methods prepares the OptiX kernels on your CPU once, and again after a Reblend or NVIDIA driver update. In my Linux test on an RTX PRO 6000 Blackwell it took about 5 seconds; a slower CPU takes longer. CUDA has no such wait.
• Windows signing. The Windows build is not code-signed, so SmartScreen warns on first launch.
• Experimental. Settings and defaults can change between versions. Check deadline work in stock Blender too.

Found something else? Write to contact@leonidaltman.com with the version line from the About box and, if you can, the .blend file.