Ok I upgraded toolbar from 1.7 to 1.8 and problem is gone :) There are a number of toolbar bugs at https://github.com/jazzband/django-debug-toolbar/issues/943

Ok I upgraded toolbar from 1.7 to 1.8 and problem is gone :) There are a number of toolbar bugs at https://github.com/jazzband/django-debug-toolbar/issues/943 https://github.com/jazzband/django-debug-toolbar/issues/943 involving keywords "slow" and "hang", not sure which it was. But the meta-issue is, the profiling tools I used were not super helpful in discovering what the issue was.