On macOS 10.15.4, but not earlier, simply build and run the current git master version of the SimpleCocoaVTK example and resize the window. It will crash with backtrace:

Crashed Thread:        0  Dispatch queue: com.apple.main-thread

Exception Type:        EXC_CRASH (SIGABRT)
Exception Codes:       0x0000000000000000, 0x0000000000000000
Exception Note:        EXC_CORPSE_NOTIFY

Termination Reason:    LIBSYSTEM, [0x2]

Application Specific Information:
assertion failure: "_needsGeometryInWindowDidChangeNotificationCount > 0" -> %lld

Thread 0 Crashed:: Dispatch queue: com.apple.main-thread
0   libsystem_kernel.dylib        	0x00007fff70536ad6 __abort_with_payload + 10
1   libsystem_kernel.dylib        	0x00007fff705383df abort_with_payload_wrapper_internal + 80
2   libsystem_kernel.dylib        	0x00007fff70538411 abort_with_payload + 9
3   libsystem_c.dylib             	0x00007fff704a380b _os_crash_fmt.cold.1 + 55
4   libsystem_c.dylib             	0x00007fff70436e62 _os_crash_fmt + 154
5   com.apple.AppKit              	0x00007fff337796f9 -[NSView(NSInternal) disableGeometryInWindowDidChangeNotification] + 229
6   com.apple.AppKit              	0x00007fff33aea004 NSOpenGLContextDetachOffScreenViewSurface + 52
7   com.apple.AppKit              	0x00007fff33aabb3b -[NSOpenGLContext update] + 267
8   org.vtk.SimpleCocoaVTK        	0x0000000103f0676b vtkCocoaRenderWindow::Start() + 139
9   org.vtk.SimpleCocoaVTK        	0x0000000103e426b4 vtkRenderWindow::Render() + 804
10  org.vtk.SimpleCocoaVTK        	0x0000000104064adf vtkOpenGLRenderWindow::Render() + 31
11  org.vtk.SimpleCocoaVTK        	0x0000000103cf762d -[CustomLayer drawInCGLContext:pixelFormat:forLayerTime:displayTime:] + 509
12  com.apple.QuartzCore          	0x00007fff42000a03 CAOpenGLLayerDraw(CAOpenGLLayer*, double, CVTimeStamp const*, unsigned int) + 1956
13  com.apple.QuartzCore          	0x00007fff42000084 -[CAOpenGLLayer _display] + 580
14  com.apple.QuartzCore          	0x00007fff41f64469 CA::Layer::display_if_needed(CA::Transaction*) + 757
15  com.apple.QuartzCore          	0x00007fff41f42716 CA::Context::commit_transaction(CA::Transaction*, double) + 334
16  com.apple.QuartzCore          	0x00007fff41f41304 CA::Transaction::commit() + 644
17  com.apple.AppKit              	0x00007fff33a5a2fd __28-[NSMoveHelper _doAnimation]_block_invoke + 1014
18  com.apple.AppKit              	0x00007fff33905a94 -[NSScreenDisplayLink _fire] + 180
19  com.apple.AppKit              	0x00007fff34052d62 ___NSRunLoopTimerCreateWithHandler_block_invoke + 34
20  com.apple.CoreFoundation      	0x00007fff3649e9b9 __CFRUNLOOP_IS_CALLING_OUT_TO_A_TIMER_CALLBACK_FUNCTION__ + 20
21  com.apple.CoreFoundation      	0x00007fff3649e51f __CFRunLoopDoTimer + 859
22  com.apple.CoreFoundation      	0x00007fff3649e007 __CFRunLoopDoTimers + 322
23  com.apple.CoreFoundation      	0x00007fff36482daa __CFRunLoopRun + 1871
24  com.apple.CoreFoundation      	0x00007fff36481ffe CFRunLoopRunSpecific + 462
25  com.apple.AppKit              	0x00007fff33a597bb -[NSMoveHelper _doAnimation] + 1349
26  com.apple.AppKit              	0x00007fff33a62225 -[NSMoveHelper _resizeWindow:toFrame:display:] + 300
27  com.apple.AppKit              	0x00007fff3397d10c -[NSWindow setFrame:display:animate:] + 818
28  com.apple.AppKit              	0x00007fff33f9dc63 -[NSWindow _zoomToScreen:isMoveToiPad:] + 449
29  com.apple.AppKit              	0x00007fff339baecb -[NSTitledFrame _handlePossibleDoubleClickForEvent:] + 234
30  com.apple.AppKit              	0x00007fff339ba960 -[NSThemeFrame mouseUp:] + 278
31  com.apple.AppKit              	0x00007fff33935969 forwardMethod + 204
32  com.apple.AppKit              	0x00007fff33935969 forwardMethod + 204
33  com.apple.AppKit              	0x00007fff340c7c1b -[NSTitlebarView mouseUp:] + 261
34  com.apple.AppKit              	0x00007fff33935969 forwardMethod + 204
35  com.apple.AppKit              	0x00007fff338a6aff -[NSWindow(NSEventRouting) _reallySendEvent:isDelayedEvent:] + 2738
36  com.apple.AppKit              	0x00007fff338a5e29 -[NSWindow(NSEventRouting) sendEvent:] + 349
37  com.apple.AppKit              	0x00007fff338a41b4 -[NSApplication(NSEvent) sendEvent:] + 352
38  com.apple.AppKit              	0x00007fff336f121f -[NSApplication run] + 707
39  com.apple.AppKit              	0x00007fff336c2ff6 NSApplicationMain + 777
40  org.vtk.SimpleCocoaVTK        	0x0000000103cf2f62 main + 34
41  libdyld.dylib                 	0x00007fff703d5cc9 start + 1

The issue is with the rightmost view, which using CALayer instead of NSView for rendering.

The initial attempt to fix this had some side effects that we ended up backing out of: !6653 (merged)

so we need a new solution.

See also: #17832 (closed) !6920 (merged)