&gt; If you&#x27;re using core.async, the main loop has a try&#x2F;catch&#x2F;rethrow. This causes Chrome Dev Tools to break in the outer loop instead of actually at the problem.<p>OMG! Is that what is causing that behaviour?! It&#x27;s frustrating (though not a show stopper) and I was unsure of the cause. Thanks for pointing that out. I will have a deeper look.