I have the same problem. This is my debug output: -[MTLDebugDevice notifyExternalReferencesNonZeroOnDealloc:]:2885: failed assertion `The following Metal object is being destroyed while still required to be alive by the command buffer 0x3260f3800 (label: ): <MTLToolsObject: 0x600000d08360> -> <IOGPUMetalFence: 0x600000d0bc60>'

I experience the same problem. It seems the default maximum width of the Form view is set. No work around yet.