Good find! This has to do with the order of execution in the runtime.
Currently, when a generator cell yields, it may resume before other variables that reference the cell have a chance to run. Hence in your notebook, the autoBox function is called before the chart is inserted into the DOM and the computed viewBox is [0, 0, 0, 0].
I’ve opened a pull request that defers the resumption of generators until after all active variables have a chance to start computing.
I’ll need to do more testing, but I believe this will fix the problem here and give more predictable behavior to yield.
In the meantime you can workaround this issue by calling autoBox again: