Would Tini help?
I'm my experience Selenium will appear to be functioning normally from the outside, but the driver completely locks and doesn't proceed at seemingly random times. I couldn't think of a sane way to detect this, killing containers seemed easier and has worked reliably so far. I'm definitely open to hearing suggestions though.
That aside though Tini looks like a good starting point for containers like mine anyways. So thanks, it does seem helpful!
I think the terminology for that is "wedged".