bokeh: Bokeh occasionally not working with Jupyter Notebook

I’m not sure what’s going on. I get this error occasionally and I may have gotten a reproducible example but I haven’t confirmed just yet.

There are no errors in the python side. Instead of a plot I see <bokeh.io._CommsHandle at 0x109b1ec18> as the output. The javascript console shows:

Kernel: kernel_restarting (b738e19a-021b-47ef-9d08-076f696147c8)
main.min.js:22329 Kernel: kernel_created (b738e19a-021b-47ef-9d08-076f696147c8)
main.min.js:22673 Starting WebSockets: ws://localhost:8888/api/kernels/b738e19a-021b-47ef-9d08-076f696147c8
main.min.js:22329 Kernel: kernel_connected (b738e19a-021b-47ef-9d08-076f696147c8)
main.min.js:22329 Kernel: kernel_ready (b738e19a-021b-47ef-9d08-076f696147c8)
(program):67 Bokeh: BokehJS loaded, going straight to plotting
cdn.pydata.org/bokeh/release/bokeh-0.11.0.min.js:3 Bokeh: setting log level to: 'info'
(program):53 Bokeh: injecting CSS: https://cdn.pydata.org/bokeh/release/bokeh-0.11.0.min.css
(program):55 Bokeh: injecting CSS: https://cdn.pydata.org/bokeh/release/bokeh-widgets-0.11.0.min.css
(program):72 Bokeh: BokehJS loaded, going straight to plotting

Could not open comm  --  Error: Class 1854dd25-3916-46bd-aab3-1729f21a403a not found in registry
main.min.js:23119 Couldn't process kernel message WrappedError(anonymous function) @ main.min.js:23119

Couldn't process kernel message WrappedError(anonymous function) @ main.min.js:23119