I noticed this too, but haven’t had a chance to dig into it much. I suspect Chrome is getting confused by the GLX fbconfigs being presented in render offload mode. They’re slightly different from what you see in non-offload mode because of limitations in how the driver is able to map NVIDIA fbconfigs to X11 Visuals on the target screen.
I suspect Chrome is getting confused by the backwards way it creates a window and then tries to find an fbconfig. There’s a comment about it in the source code here, and I have a feeling that doing what the comment suggests would fix the problem:
https://chromium.googlesource.com/chromium/chromium/+/master/ui/gl/gl_surface_glx.cc#168
// TODO(kbr): this is not a reliable code path. On platforms which
// support it, we should use glXChooseFBConfig in the browser
// process to choose the FBConfig and from there the X Visual to
// use when creating the window in the first place. Then we can
// pass that FBConfig down rather than attempting to reconstitute
// it.