This is related to T71445 and the like (e.g. T71519)
We've had a couple of instances where common.js has been throwing exceptions is certain configurations (e.g. using a deprecated IE method in IE11 which caused T97788). If common.js crashes most people don't notice because it usually only disables a few progressive enhancements or browser bug workarounds, but more critical features such as VisualEditor or MediaViewer can suffer from these fatal exceptions.
These errors could be rethrown as warnings or logged.